Slow email sending from cPanel SMTP

I received a few complaints from different people, that sending of email messages is really slow. This didn’t make any sense, because no modifications were made on the server.

After an hour, I found that this was caused by Exim setting “Delay SMTP Transaction”. Quoting cPanel: The SMTP receiver will wait a few additional seconds for a connection when it detects spam messages in order to reduce inbound spam. 

So it’s another weapon to fight spam mail, but it makes sending slower.

You can disable this feature in Exim Configuration Manager -> ACL Options -> Introduce a delay into the SMTP transaction for unknown hosts and messages detected as spam.

When disabled, your emails should be fast again.

CSF – whitelist user from SMTP_BLOCK

CSF features great option SMTP_BLOCK which block outgoing SMTP for all users except root, exim and mailman. I had a problem with one user which was using MailChimp as mass mailing within their application. Because of SMTP_BLOCK it wasn’t working. Disabling SMTP_BLOCK globally is not recommended, you can white list users for which you would like to allow sending.

Go to your CSF settings and find SMTP_ALLOWUSER. Then add user which should be allowed (users separated with coma). Don’t forget to restart CSF.

cPanel: Your server does not support the connection encryption type you have specified

If you’re getting message like “Your server does not support the connection encryption type you have specified” when try to set up email in your Outlook, then chances are that your cPanel mail server has disabled some needed encryption types.

By default, cPanel disables all those protocols: SSLv2, SSLv3, TLSv1, TLSv1.1. SSL2 and SSL3 should be disabled at all costs, but you may not get away with TLS 1.1 or even TLS 1 being disabled.

To enable TLS 1 and TLS 1.1 in your Exim, login as admin in your cpanel and then: Home -> Service Configuration -> Exim Configuration Manager. Select second option so you can insert your own directives and add this:

 +no_sslv2 +no_sslv3

malware acl condition: clamd: unable to send file body to socket (127.0.0.1)

If you see error like this in your mail logs, than chances are that your ClamAV is not able to process attachments files larger than limit set in clamav configuration. In this case, sender which sent email with larger attachment to your server, will get something like this in respond:

[10.10.10.10] #<[10.10.10.10] #5.0.0 smtp; 5.4.7 - Delivery expired (message too old) [Default] 451-'Temporary local problem - please try later' (delivery attempts: 75)> #SMTP#

In your mail log you’ll see something like this:

+++ 1e248B-000NMy-T6 has not completed +++
1969-08-15 01:40:21 1e248B-000NMy-T6 malware acl condition: clamd : unable to send file body to socket (127.0.0.1)
1969-08-25 01:40:21 1e248B-000NMy-T6 H=some.hostname.com [1.1.1.1] X=TLSv1:RC4-SHA:128 CV=no F=<prvs=449d2f142=senders@email.com> temporarily rejected after DATA

To solve this, open your clamav.conf file (/etc/clamav.conf or find your location) and change value for StreamMaxLength according to your needs. Default value is 25M.

Don’t forget to restart your ClamAV.

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