Le 2023-05-03 15:02, Sam Darwin via Boost a écrit :
Mailgun has been in production for many years. It costs $500 per month to send smtp messages. It's a reasonable idea to try out another service that's only 5% of the cost.
Thanks for the detailed answer. From what is seen, it does indeed looks like amazon ses is sending emails with different message ids to each participant in the mailing list. Mailgun, on the other hand, was keeping the original message id in the email.
But at the same time, it's not impossible to switch back to mailgun, if threading is partially disrupted, and we can't find a solution.
Now that the source of the problem has been identified, i hope a solution can be found. Like Phil noted, mailgun is indeed very expensive. Best regards, Julien