Bash – How to remove all messages from exim mail queue from a certain user/email

Modern major mail services score spamminess based on multiple reputation factors, if available.

If the only factor is your IP and you don't mail often, this might be "the reputation of the /24 my IP is in". If you mail a lot, you might get your own reputation.

The easiest way to get reputation which "drowns out" the IP reputation of your netblock is to set up DKIM. Send your mails signed. This will establish a per-domain reputation, instead of per-IP reputation, and provides more signal to the automated scoring systems.

The more you work to help the recipients of your email figure out who you are and how trustworthy you are, the more signals they have to work with and the better a job the automated systems can do in deciding that you're legitimate, unlike whoever else bought a virtual machine in the same netblock, pumped out spam and then left, bills to hosting service unpaid and everyone else's reputation tarnished.

[some years later]: I wrote a blog post a couple of years back, walking through a lot of the steps needed to be able to more reliably send to large mail providers: https://bridge.grumpy-troll.org/2020/07/small-mailserver-bcp/

Have you checked out this option:

Percentage of email messages to queue and retry for delivery

This configuration option allows you to define how overages are handled when a domain exceeds the maximum number of emails allowed per hour. By default, additional messages are queued for delivery and sent in the next hour. This option is only available to the root user and to resellers that have root privileges. The configuration data for this option is stored in /var/cpanel/cpanel.config.

The value you configure here is compared against the value set in Max hourly emails to determine whether an outgoing message should be queued and resent later or discarded. For example, if you set this value to 125%, then once the domain reaches its hourly limit, Exim will queue any additional messages, up to 125% of the Max hourly emails value. Once the account reaches 125% of the Max hourly emails value, any additional outgoing messages are discarded.

You may use this feature to discard all outgoing messages once the domain has reached its limit by setting the The percentage of email messages (above the account’s hourly maximum) to queue and retry for delivery value to 100.