From Spry Wiki
In my never ending quest to keep exim running as smoothly as possible I have stumbled across a couple of settings that seem to have helped. One of the problems with running applications in a virtual environemt is that when memory load gets to high processes fail or die. Having Exim fails means no mail and this is rarely a desired occurance (unless perhaps it's Friday at 4:30). Two settings that can prevent this from happening are;
Option: deliver_queue_load_max Type: fixed-point Default: unset If this option is set, its value is used to determine whether to abandon a queue run, instead of the value of `deliver_load_max'.
Option: smtp_accept_max Type: integer Default: 20 This specifies the maximum number of simultaneous incoming SMTP calls that Exim will accept. It applies only to the listening daemon; there is no control (in Exim) when incoming SMTP is being handled by `inetd'. If the value is set to zero, no limit is applied. However, it is required to be non-zero if 'smtp_accept_max_per_host' or `smtp_accept_queue' is set.
For more info on these settings read http://www.fastmirrors.org/exim/exim-html-3.00/doc/html/spec_11.html
This specifies the maximum number of simultaneous incoming SMTP calls that Exim will accept. It applies only to the listening daemon; there is no control (in Exim) when incoming SMTP is being handled by `inetd'. If the value is set to zero, no limit is applied. However, it is required to be non-zero if `smtp_accept_max_per_host' or `smtp_accept_queue' is set.
By changing these from the default you can 'throttle' Exim. You need to make these changes to the exim.conf file and you have to do it through WHM (https://youdomain.com:2087) From the main page go to Main >> Service Configuration >> Exim Configuration Editor. Towards the bottom of the screen you will see a box lableled "Advanced Editor Instructions" Click on the button labeled "Advanced Editor". below the line labeled "exim.conf" you will see a blank box where you can enter data. Paste or type the following exactly the way it is shown;
smtp_accept_max = 50 deliver_queue_load_max = 2
This will change the defaults from
smtp_accept_max = 100
smtp_accept_max = 50
deliver_queue_load_max = 3
deliver_queue_load_max = 2
Then click "Save" at the bottom of the screen. The changes will be written to /etc/exim.conf and Exim will restart. If you have any problems you can change them back to the defaults by changing the values to;
smtp_accept_max = 100 deliver_queue_load_max = 3