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We use a mail server that runs Exim to send mailings to our clients. Sendblaster is used to connect to the server and send the emails to a list of clients.

Currently we use two instances of Sendblaster on separate PCs to split up the load. It is possible speed things up by have more instances or by increasing the connections value in Sendblaster?

How many simultaneous connections can Exim handle at a time?

  • The answer depends on a few things. Are all of your servers behind the same SNAT, in the same netblock, using the same sending domain name? These questions are related to rate limits on the receiving side of whomever you are talking to. Do the people you are emailing whitelist your IP's? There are many other facets to this, but people would need to know that first. – Aaron Feb 05 '21 at 20:56
  • What is currently your actual bottleneck ? Is it actually generating unique emails (which can be computationally expensive)? Is the process stalling because you are generating mails faster than exim will accept them? Can exim send out the messages as or more quickly then you generate them, or are you already only filling up the mail queu and should you be tuning exim rather than Sendblaster to get mails more quickly into the recipients Inbox? https://www.exim.org/exim-html-current/doc/html/spec_html/ch-how_exim_receives_and_delivers_mail.html – Bob Feb 06 '21 at 07:28

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How many simultaneous connections can Exim handle at a time?

That is governed by the exim smtp_accept_max setting which has a default value of 20 concurrent incoming connections : https://www.exim.org/exim-html-current/doc/html/spec_html/ch-main_configuration.html

Bob
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