I'm not sure if it just me, but I am not 100% clear on what each of the CiviMail mailer settings do when combined together?

Mailer Batch Limit: The total number of emails that will go out on each CiviMail run? If multi-threading does this number multiply by the number of threads or does this number get shared out over the number of threads?

Mailer Throttle time: The sleep time in micro seconds between each individual email? If multi-threading does this time multiply by the number of threads or does this number effectively become redundant because multiple jobs are all running at this speed meaning emails are actually sending faster than this value?

Mailer Job Size: The size of smaller lists the entire list of contacts will be split into to create threads. See point about Mailer Batch Limit, does this mean the batch amount will be processed from each job.. or will the batch amount be split over all the jobs?

Mailer CRON job limit: The number of cron jobs fired off.. how is this determined? number of jobs or number of spare processes?

In short, I think it could be clearer what is going on?

CiviMail Mailer Settings

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    I found some logical guesswork on this by @totten that may be useful although he does say it's not based on looking at the code and it was written back in 2015. Aug 3, 2019 at 7:38
  • Those notes explain a lot. Nov 13, 2019 at 8:55

1 Answer 1


There is some more detail in the documentation.

And there are also notes from Tim on Github. Those notes share the idea that it is confusing. However I do think it answers your question. It would have been helpful though when those notes are added to the documentation.

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