Process more (or less) emails concurrently

Attention

Processing more emails concurrently requires more RAM, please make sure you have enough RAM to handle them, otherwise ClamAV may exit randomly due to no enough memory (for ClamAV).

Amavisd-new is content filter, it invokes SpamAssassin and ClamAV for spam/virus scanning, it also offers additional features like DKIM signing and verification.

In Amavisd config file, $max_servers sets the number of concurrent Amavisd processes and it must match the number set in /etc/postfix/master.cf maxproc column for the smtp-amavis service. Sample settings:

# Amavisd config file:
#   - on RHEL/CentOS: /etc/amavisd/amavisd.conf
#   - on Debian/Ubuntu: /etc/amavis/conf.d/50-user
#   - on FreeBSD: /usr/local/etc/amavisd.conf
#   - on OpenBSD: /etc/amavisd.conf

$max_servers = 4;

# File: /etc/postfix/master.cf

smtp-amavis unix -  -   -   -   4  smtp
    ...

Both values should be identical for two reasons: If Amavisd offers more processes than Postfix will ever use, Amavisd wastes resources. On the other hand, if Postfix starts more dedicated transports than amavisd can handle simultaneously, e-mail transport will be refused and logged as error.

If many emails stalled in mail queue (check with command postqueue -p), and your server has powerful CPU and memory, you can increase the number of concurrent Amavisd processes, so that it can process more emails at the same time. Sample setting:

# File: /etc/amavisd/amavisd.conf

$max_servers = 10;

Restarting Amavisd service is required.

# File: /etc/postfix/master.cf

smtp-amavis unix -  -   -   -   10  smtp
    ...

Note: If you don't want to modify /etc/postfix/master.cf, it's ok to set smtp-amavis_destination_concurrency_limit = 10 in /etc/postfix/main.cf instead.

Restarting Postfix service is required if you modified /etc/postfix/master.cf, reloading OR restarting is required if you modified /etc/postfix/main.cf.

References: