Installation of Exim4, DoveCot, SquirrelMails
This is for Debian 7 Wheezy, but seems to work for Debian 10 Buster too
(old Installation of Exim4, DoveCot, SquirrelMails, Debian 5, Debian 6)
Goals
- Using Debian 7 Wheezy
- Exim 4 as mail server
- Using self created certificate
- Dovecot for imap access
- Horde as web client
- SpamAssassin for spam filtering
- Access from
- Thunderbird
- Outlook: works out of the box, but you have to have certificates which match the domain names
- Backup of mails to a different system
- virtual users
- remote management of sieve filters (still not working)
Exim 4
install
We will use the heavy version to be able to later integrate SpamAssassin.
apt-get install exim4-daemon-heavy
(I don't use this anymore: If you can start programs with X-Server, you would like to get geximon:
apt-get install geximon xauth
Remember to ssh with "-X" or "ForwardX11 yes" in your config)
paniclog
If you get paniclog entries like "address already in use", find out about the other process with
netstat -4anp | grep 25
Chances are, it is something about sendmail. Do
which sendmail
and "ls -l" on the result like
ls -l /usr/sbin/sendmail
or just (ticks, not single quotes)
ls -l `which sendmail`
Chances are, it is a link to exim4 and the installation went wrong. Happens every time for me. Remove the paniclog and restart the server. Check the log /var/log/exim4/mainlog
If it is not the above, perhaps you need to remove the sendmail(-bin) package.
validating
Have a look at the ports:
netstat -apn | grep exim
If you have exim4 listen on port 25, you should be ok.
- add at least one local user so you can set him as receiver for postmaster etc in the next step
Now you should reconfigure exim4
dpkg-reconfigure exim4-config
- internet site
- accept the domain name if you don't know better
- IP addresses to listen to:
- leave this empty or make sure you include the external ip
- ::1 the IP6 variant, if you keep this empty, don't bother now
- final destination: your domains
- domains to relay for: normally none (empty)
- machines to relay for: normally none (empty)
- DNS queries minimal: your choice (default: no)
- delivery method: maildir in home directory
- split: your choice (default: no !!!) The main difference is, where will you later put your modifications
- non-split: /etc/exim4/exim4.conf.localmacros
- split: /etc/exim4/conf.d/main/000_localmacros
- root/postmaster: select the above created user, should really read his mail
Now send a mail:
echo Hello You | mail <user>@<OTHER-domain> -s test-1
You should receive the mail at your account at the OTHER domain.
open firewall
If you have a firewall, open it for incoming at port 25. For example ufw:
ufw allow smtp
or firehol in /etc/firehol/firehol.conf
server smtp accept
An example for a whole firehol.conf:
FIREHOL_LOG_PREFIX="firehol: " server_mySsh_ports="tcp/23" client_mySsh_ports="default" interface any world protection strong policy drop client all accept server ICMP accept server mySsh accept server https accept server imaps accept server smtp accept server imap accept server smtps accept
TLS for SMTP
If you will have different mail domains at one ip you will get into problems with Outlook if you do not have one certificate per domain where the certificate matches the domain name. (TODO)
- install openssl (for certificate) and swaks (for tests) and libnet-ssleay-perl
apt-get install openssl swaks libnet-ssleay-perl
- edit the cert creation script, check at least the DAYS value. 7300 would be 20 years.
vi /usr/share/doc/exim4-base/examples/exim-gencert
- execute the script
/usr/share/doc/exim4-base/examples/exim-gencert
- create file /etc/exim4/exim4.conf.localmacros (non-split!) with
MAIN_TLS_ENABLE = 1
- reload exim
/etc/init.d/exim4 reload
- test it locally
swaks -f yourMail@YourDomain.com -t yourMail@YourDomain.com -tls -s localhost
- What would be bad:
Host did not advertise STARTTLS
sasl for system login
Currently we want system users and system user passwords, so we use SASL:
- install it
apt-get install sasl2-bin
- enable for system restart in /etc/default/saslauthd
START=yes
- add exim user to sasl group
adduser Debian-exim sasl
- start sasl
/etc/init.d/saslauthd start
enable exim to ask clients for passwords if they want to SEND mails
in /etc/exim4/exim4.conf.template enable the following 2 sections
plain_saslauthd_server:
driver = plaintext
public_name = PLAIN
server_condition = ${if saslauthd{{$auth2}{$auth3}}{1}{0}}
server_set_id = $auth2
server_prompts = :
.ifndef AUTH_SERVER_ALLOW_NOTLS_PASSWORDS
server_advertise_condition = ${if eq{$tls_cipher}{}{}{*}}
.endif
login_saslauthd_server:
driver = plaintext
public_name = LOGIN
server_prompts = "Username:: : Password::"
# don't send system passwords over unencrypted connections
server_condition = ${if saslauthd{{$auth1}{$auth2}}{1}{0}}
server_set_id = $auth1
.ifndef AUTH_SERVER_ALLOW_NOTLS_PASSWORDS
server_advertise_condition = ${if eq{$tls_cipher}{}{}{*}}
.endif
- activate it
update-exim4.conf && /etc/init.d/exim4 reload
- add one of the system users you will want to add anyway
- after installation of dovecot try for example to send a mail with Thunderbird, you should get asked to accept the certificate and give the password
virtual users
Source: https://www.organicdesign.co.nz/Configure_mail_server#Setting_up_mail_users
in exim4.conf.template set domainlist to
vi /etc/exim4/exim4.conf.template domainlist local_domains = @ : @[] : localhost : partial-lsearch;/etc/exim4/virtual.domains
after section "real_local" add
virtual:
driver = redirect
allow_defer
allow_fail
data = ${lookup{$local_part@$domain}lsearch*@{/etc/exim4/virtual.users}}
domains = partial-lsearch;/etc/exim4/virtual.domains
retry_use_local_part
create the file /etc/exim4/virtual.domains
example.com example.net
reload settings
update-exim4.conf && /etc/init.d/exim4 reload
change /etc/exim4/virtual.users, you don't have to restart the server for this
regularuser@example.com : localuser@localhost forwardinguser@example.com : someuser@example.org foo@example.com : :fail: Foo no longer lives here. bar@example.com : :blackhole: *@example.com : catchall1@localhost
regularuser@example.net : localuser2@localhost forwardinguser@example.net : someuser2@example.org *@example.net : catchall2@localhost
If you have the local user smith but you want only to allow smith to get mail via huber@example.com, then use the following pattern:
huber@example.com : smith@localhost *@example.com : :fail: Your message
disable ipv6
to be able to send messages to providers like google, you will have to support ipv6 completely or not at all. So:
add to /etc/exim4/update-exim4.conf.conf
disable_ipv6='true'
add to /etc/sysctl.conf
net.ipv6.conf.all.disable_ipv6 = 1 net.ipv6.conf.default.disable_ipv6 = 1 net.ipv6.conf.lo.disable_ipv6 = 1 net.ipv6.conf.eth0.disable_ipv6 = 1
restart the server
shutdown -r now
set some receivers to external mail accounts
- edit /etc/aliases
- change the entries to something you like, for example
root : you@yourDomain.com
- then run
newaliases
- perhaps you just need to allow root@your-domain.com as valid mail receiver
DoveCot
- allow in your firewall, for example for ufw
ufw limit imap
or for firehol in /etc/firehol/firehol.conf
server imap accept
Don't forget
firehol start
- install it
apt-get install dovecot-imapd
- use same directory for mail as exim4:
vi /etc/dovecot/conf.d/10-mail.conf
mail_location = maildir:~/Maildir #mail_location = mbox:~/mail:INBOX=/var/mail/%u
/etc/init.d/dovecot restart
- first test (look for "Dovecot ready")
telnet localhost 143
- remote test (look for "Dovecot ready") from another computer
telnet <domain> 143
- remote tls test
openssl s_client -connect <domain>:143 -starttls imap
folders below inbox
Attention: Only customize this for NEW servers where ALL mailboxes are NEW. Otherwise, use the same settings as the old server. Exception: if you know what you are doing :-)
If you want the folders junk, sent etc. below the inbox, then do the following but keep in mind that is is not possible to just copy mail/ or Maildir/ from another server AND change the separator etc.
vi /etc/dovecot/conf.d/10-mail.conf
search for "namespace inbox" and inside that scope change
separator =
to
separator = /
Then open
vi /etc/dovecot/conf.d/15-mailboxes.conf
and have it look like the following (INBOX/ and auto=subscribe and \Archive), do NOT reformat it to something like:
mailbox INBOX/Junk
{
special_use = \Junk
auto=subscribe
}
This is considered an invalid format by Dovecot :-(
This is the normal format:
namespace inbox {
mailbox INBOX/Drafts {
special_use = \Drafts
auto=subscribe
}
mailbox INBOX/Junk {
special_use = \Junk
auto=subscribe
}
mailbox INBOX/Trash {
special_use = \Trash
auto=subscribe
}
mailbox INBOX/Sent {
special_use = \Sent
auto=subscribe
}
mailbox INBOX/Archive {
special_use = \Archive
auto=subscribe
}
}
switch server
You can copy "mail" or "Maildir" directories from one server or account to the other. If you copy between servers you will have to have the same prefix/separator in both locations. Or you have to understand this: http://wiki2.dovecot.org/Namespaces or something like it. Whatever you do, after the copy of a Maildir, do
chown -R newUser:newUser Maildir
Spam Assassin
the following is from sysadmin world
- install spamassassin and the exim filter
apt-get install sa-exim spamassassin
- old debian (7): start on each boot:
vi /etc/default/spamassassin ENABLED=1
- new debian (10): start on each boot:
update-rc.d spamassassin enable
- new debian (10):
vi /etc/default/spamassassin CRON=1
- What about Debian 8 and 9? No idea.
- start
service spamassassin start
- in /etc/exim4/exim4.conf.template at the top in MAIN CONFIGURATION SETTINGS add:
local_scan_path = /usr/lib/exim4/local_scan/sa-exim.so
- enable the connector in /etc/exim4/sa-exim.conf. Please be careful, there are some lines with SAEximRunCond but only one with SAEximRunCond: 0. Comment this line out.
#SAEximRunCond: 0
Logging:
SAEximDebug: 0
- activate changes in /etc/exim4/exim4.conf.template
/usr/sbin/update-exim4.conf
- restart exim
/etc/init.d/exim4 restart
Let Spam Assassin learn from your folders
Spam Assassin can learn what is junk and what is ham (not junk) from your folders, if the users of your mail server put junk mails into certain folders and good mails into certain other folders. If Thunderbird is being used, it is easy.
crontab -e 32 1 * * * . /etc/profile && /usr/bin/sa-learn --spam /home/*/Maildir/.INBOX.Junk/ > /dev/null 45 2 * * * . /etc/profile && /usr/bin/sa-learn --ham /home/*/Maildir/.INBOX.Archive* > /dev/null
This way your Spam Assassin will learn each night more. It is important to realize that Spam Assassin does not put junk into certain folders. It will only mark the messages as junk. You have to configure your e-mail program to trust Spam Assassin headers and put marked mails into its junk folders.
SquirrelMail
SquirrelMail does not exist for Debian 10, here the old instructions for Debian 7: SquirrelMail Installation for Debian 7
Do NOT use this! I just point to it and keep it because I don't want to delete it.
Horde (Webmail, instead of SquirrelMail)
info
Please be careful in this section. I am not 100% sure what I did here. Make sure you have created a real user who will be using his mail account later because you need to give his name as the first admin.
install
Make sure you have the locales installed (should do nothing, but...just in case):
apt-get install locales
Configure them:
dpkg-reconfigure locales
I always keep en_US.UTF-8 and the locale for my country (de_DE.UTF-8).
Install horde and the PDO driver for sqlite for PHP - I hope this made sense ;-)
apt-get install php-horde-webmail php7.3-sqlite3
setup
Modify the port for ssl use:
vi /usr/share/horde/config/conf.php.dist // $conf['server']['port'] = 80; $conf['server']['port'] = 443;
prepare the database directory
mkdir /usr/share/horde/database chown -R www-data:www-data /usr/share/horde/database
call the setup
webmail-install > sqlite > /usr/share/horde/database/horde
At some point after this the database file will exist
ls -l /usr/share/horde/database/horde
If it exists and looks like this:
-rw-r--r-- 1 root root 1892352 Nov 20 09:43 horde
then it's wrong. And you should do the same stuff as always:
chown www-data:www-data /usr/share/horde/database/horde chmod 600 /usr/share/horde/database/horde
HINT HINT HINT: if your horde login succeeded but you get the information that a read-only database can't be written into... then you know you forgot it!
doing weird stuff in the hope it will activate ssl
You already changed the default port above to 443. That was in this context too.
Check the rights for the folders (look for "Directory") and consider to only allow /usr/share/horde
vi /etc/apache2/apache2.conf
<Directory />
Options FollowSymLinks
AllowOverride None
Require all denied
</Directory>
<Directory /usr/share/horde>
AllowOverride None
Require all granted
</Directory>
<Directory /var/www/>
Options Indexes FollowSymLinks
AllowOverride None
Require all denied
</Directory>
Disable the normal port 80:
vi /etc/apache2/ports.conf
# Listen 80
<IfModule ssl_module>
Listen 443
</IfModule>
<IfModule mod_gnutls.c>
Listen 443
</IfModule>
Enable some mods:
cd /etc/apache2/mods-enabled ln -s ../mods-available/socache_dbm.load ln -s ../mods-available/socache_memcache.load ln -s ../mods-available/socache_shmcb.load ln -s ../mods-available/ssl.conf ln -s ../mods-available/ssl.load
Disable the default (port 80/html) site and enable the ssl default config:
cd /etc/apache2/sites-enabled rm 000-default.conf ln -s ../sites-available/default-ssl.conf
Restart apache:
/etc/init.d/apache2 restart
.htaccess
Depending on your circumstances (only you as user, more security needed...) you can consider to add a .htaccess file to your /usr/share/horde directory. Check out this for some basic info: Apache 2, quickly protect directory with password
done?
Try to reboot your system and then connect to
https://<your-domain>/horde/
Errors
The "solutions" to these errors are mostly hacks and I have no idea if they make your system unsafe. Sorry. So... if you know what you are doing, think before you do it.
Could not instantiate PDO. PDOException: could not find driver
apt-get install php-sqlite3 /etc/init.d/apache2 restart
Line 142: old
$data = @fread($fp, filesize($this->cache_file));
new:
$data = false;
$file_size = @filesize($this->cache_file);
if ( ($file_size !== false) && ($file_size > 0) )
$data = @fread($fp, $file_size);
if ( ($data !== false) && (strlen($data) > 0) ) {
AH01630: client denied by server configuration: /var/www/html/imp
cd /usr/share/horde chown -R -L www-data:www-data *
vi /etc/apache2/apache2.conf
old:
<Directory /var/www/>
Options Indexes FollowSymLinks
AllowOverride None
Require all denied
</Directory>
new:
<Directory /var/www/>
Options Indexes FollowSymLinks
AllowOverride None
Require all granted
</Directory>
Call to undefined function each()
"each" does not exist anymore, it seems.
Below I'll change
while (list($i, $arg) = each($args)) {
into
foreach ($args as $i => $arg) {
(source)
old:
while (list(,$ob) = each($overview['overview'])) {
new:
foreach ($overview['overview'] as $i => $ob) {
old:
while (list($id, $info) = each($render_part)) {
new:
foreach($render_part as $id => $info) {
old:
while (list($id, $part) = each($msgtext)) {
new:
foreach($msgtext as $id => $part) {
Backup
If you have on some server elsewhere a rsnapshot installation running, you can just add your mail server in your /etc/rsnapshot.conf
backup root@server-mail:/etc/ server-mail/ backup root@server-mail:/var/www/ server-mail/ backup root@server-mail:/home/ server-mail/
For the above to work you will need the following:
- the backup server must be able to connect to the mail-server with ssh with keys, without passwords
- the .ssh/config must have an entry like this:
Host server-mail
HostName 123.123.123.123
User root
Port 22
ForwardX11 no
IdentityFile /root/.ssh/id-rsa-server-mail
Moving Server
If you are moving files from one server to the other, then this section is for you.
Create a local ssh key, paste the public part into the authorized_keys file of the old server.
- domains?
vi /etc/exim4/virtual.domains update-exim4.conf && /etc/init.d/exim4 reload
- virtual users?
/etc/exim4/virtual.users
- add all users to the system
adduser <username>
- aliases
vi /etc/aliases root : you@yourDomain.com newaliases
- copy mail directories
cd /home adduser user1 scp -r old-mail:/home/user1/Maildir/ user1/ chown -R user1:user1 user1/Maildir
- depending on your system, perhaps get the .htaccess file from your old system AND the file with the password and remember the rwx rights:
ls -la /usr/share/horde/.htaccess ls -la /etc/apache2/.passwd
DNS
MX / A / PTR
Make sure you have the needed DNS entries.
| Hostname | Type | Address |
|---|---|---|
| @ | MX (Mail) | mail.example.com |
| A (Address) | 41.42.43.44 | |
| 41.42.43.44 | PTR (reverse DNS) | mail.example.com |
The PTR is sometimes in the settings for the machine, not in the settings for the domain.
Make sure https://whatismyipaddress.com/blacklist-check does not contain the IP of your mail server.
Make sure you have the fully qualified hostname in your /etc/hosts as first entry in the line with the real IP, something like:
127.0.0.1 localhost localhost.localdomain ::1 localhost localhost.localdomain 278.241.130.121 imap.yourdomain.com imap xxxx:xxxx:xx::xxxx:xxxx imap.yourdomain.com imap
Check the MX entry:
dig +noall +answer -t MX yourdomain.com
The answer should be the fully qualified name of your mailserver like
imap.yourdomain.com
Check domain -> ip with dig some (ca. 24) hours after you changed it:
dig +noall +answer -t ANY <hostname> dig +noall +answer -t ANY imap.yourdomain.com
The answer should be the correct IP.
Check the qualified hostname of your server locally:
hostname -f
If the answer is
imap.yourdomain.com
then you are good, if the answer is
imap
then you have to fiddle with the hosts file (See above).
SPF
It seems to be needed by some mail servers so you can send them mail. There are many possible variants, using ips, names or using an automatic entry. There must be only ONE SPF entry for your domain. If you need more data, edit the entry, do NOT create multiple SPF entries.
One working simple version for simple servers (replace 1.1.1.1 with the ip of your server):
Hostname: @ (or whatever you use for "all" entries) Type: "txt" (preferred) or "SPF" Value: v=spf1 ip4:1.1.1.1 -all
DKIM
(GoogleMail wants a key of 1024 bits or longer)
(source)
- Start an ssh session and go to /etc/exim/
- Generate a private and public key to sign your messages with openssl:
openssl genrsa -out dkim.private.key 1024
- Extract the public key from the private key
openssl rsa -in dkim.private.key -out dkim.public.key -pubout -outform PEM
- Open /etc/exim4/exim4.conf.localmacros to modify it:
DKIM_DOMAIN = ${lc:${domain:$h_from:}}
DKIM_SELECTOR = x
DKIM_PRIVATE_KEY = /etc/exim4/dkim_rsa.private
DKIM_CANON = relaxed
- Restart Exim
/etc/init.d/exim4 restart
- Adjust your DNS settings, create a TXT setting specifying your DKIM (If you changed "dkim_selector" under "Host", "x" will need to be adjusted accordingly.):
Host: x._domainkey txt value: v=DKIM1; p=<your public key>
How to test:
Then: send an email from this address to an external email and check if both SPF and DKIM are specified correctly in the header. You should see "spf=pass" and "dkim=pass" as well as other configurations depending on which email provider you send to. Hotmail and GMail are both good to confirm these settings.
DMARC
TODO
Email Deliverability
How it works:
- Step 1: Send an email to ping@tools.mxtoolbox.com
- Step 2: Once you have sent that message it will reply. Click the link: "View your full Deliverability Report"
Outlook / Windows Mail Problems
vi /etc/exim4/exim4.conf.localmacros MAIN_TLS_TRY_VERIFY_HOSTS =
update-exim4.conf && /etc/init.d/exim4 reload
Custom certificate
Add "Outbox" as favourite, then you get the exclamation mark for the failed send and can press it and select to use the "bad" certificate. Then you restart Mail and it should be ok.
Sieve Filter (not working correctly yet)
You can add the ability to create filters which do stuff on the server. Like moving certain mails to certain folders. For example everything from @amazon.de goes to INBOX/Amazon.
This is working but the installation has only be done once so far, so it is kind of a "test in progress":
Don't be confused Sieve and ManageSieve are distinct.
Sieve is a kind of programming language to define mail filters. An interpreter is shipped by default with dovecot.
ManageSieve is a protocol to externally edit Sieve script. To my knowledge dovecot does neither ship or enable ManageSieve by default. The dovecot ManageSieve implementation is called pigeonhole (https://github.com/dovecot/pigeonhole) and the documentation including configuration instructions can be found here (https://doc.dovecot.org/admin_manual/pigeonhole_managesieve_server/)
If you check the Debian packages, you can see dovecot-core suggest dovecot-sieve but it does not suggest dovecot-managesieved. This means dovecot-managesieved won't be installed by default.
-- Thomas Schmid
install sieve filter
- install the new sieve
apt-get install dovecot-managesieved
- boot the system (multiple times or wait or change stuff with the help of good ol Google until the next item is valid)
shutdown -r now
- validate something is listening on port 4190 (I grep for dovecot instead of 4190 to see if everything seems ok)
netstat -4lpn | grep dovecot
- open your firewall for port 4190
[...] server_mySieve_ports="tcp/4190" client_mySieve_ports="default" interface any world protection strong policy drop client all accept server ICMP accept server ssh accept server imaps accept server smtp accept server imap accept server smtps accept server mySieve accept
Something is missing here! The filters can be executed with the manual command but they are not active for incoming mail.
create sieve filter
Easiest way to use this feature now is to use sieve. It worked well for me when I got from the releases page the archive for my OS. For example in my case: sieve-0.5.3-win32-x64.zip
There you can create filters in the script tab. If you want to copy/paste existing filters easily, use the source tab. Example:
#move mail from Amazon to their own folder
require "copy";
require "mailbox";
require "imap4flags";
require "fileinto";
if address :contains "From" "@amazon.de"{
fileinto "INBOX/Amazon";
}
Save this, then test it with
- go to your mail server
ssh your-mailserver
- switch to the directory where the sieve filter is, so you don't have to use paths in your commands
cd /home/YOUR-USER/sieve
- show the filter(s)
ls -l
- simulate the execution
sieve-filter -u YOUR-USER Move-Amazon.sieve INBOX
- execute the filter for real
sieve-filter -eW -u YOUR-USER Move-Amazon.sieve INBOX
Make sure the target folder exists or add a rule to create the folder. If nothing happens, make sure your folders are accessed correctly. Is "Amazon" under INBOX or parallel to it? Etc.
You can google for more filters or just create your own.
Misc
Check for space used and left
Free space
How is the situation for the system?
df -hT
This will give you a list of mounts, one of them is the one you are using for the mails of your users. Check if there is enough free space.
Used Space
You get an overview of the space used by mails by doing:
du -csh /home/*
This is of course only valid if users can't ssh or ftp to the server. In that case you'd have to use something like /home/*/Maildir/.
You could put something like this in your cron to get once a month a report.
0 12 1 * * . /etc/profile && du -csh /home/* | sort -h | mail root -s "Space used by mails: du /home"
This works - of course - only if your root's mails are forwarded to a real address (yes, do this!) or regularly read locally. (HAHA, as if!)
Usernames
If you are using the virtual users from this setup, then you are free to have any e-mail for any username. This is something you could use to improve the security of the accounts. Often servers are attacked where the attacker uses the pre-@ part of the e-mail-address as username and a dictionary-attack for the password.
If you have the e-mail-address huber@world.com, people will attack with username huber and passwords from a dictionary of some kind. But what if use huber has the login name abcdefghij1234567?
The attacker would have to test each password for each tested username which would have to come from some kind of dictionary too.
The users should not really care. If the password is complicated enough to have to be copy/pasted to avoid errors, why not do the same for the username?
Keep in mind that usernames in Linux should only use digits/lowercase letters/'-' and always start with a lower case letter. I'd avoid '-' too, but that is my preference after reading of certain tools where the devs forgot to implement the correct use of '-' in usernames.
In case you give out new accounts, consider to use weird letter/digit combinations for the username.
In case you want to change existing accounts, you'll have to do at least two changes:
- Rename a user / change username
- Change the entry in /etc/exim4/virtual.users
Perhaps do a restart of the system after the changes, just in case tools like dovecot use caches.
Journal
If you are short on space, you might have to look at /var/log/journal/.
If you don't have that directory, then don't bother. Stop reading this.
If the files there are too many and you really don't want to "waste" 3GB or something for these files, then you could do the following:
- edit /etc/systemd/journald.conf
# for example SystemMaxUse=100M
- restart the service
service systemd-journald restart
SpamAssassin Complex regular subexpression recursion limit
If you get the following message for certain mails:
Complex regular subexpression recursion limit (32766) exceeded at /usr/share/perl5/Mail/SpamAssassin/HTML.pm line 753
then go to the given file and line and replace
if ($text !~ /^(?:[ \t\n\r\f\x0b]|\xc2\xa0)*\z/s) {
with
if (do {(my $tmp = $text) =~ s/(?:[ \t\n\r\f\x0b]|\xc2\xa0)//gs; length($tmp)}) {
