Briefly looked at the thread over there, and somebody described it as a regression? Could you pinpoint where/when the regression has happened?

@Ocramius probably this is not a regression. osTicket just started to use LM in June 2022 (they had something totally another before), so some of the users just updated, and some - just installed osTicket from the scratch.

I'm one of those who try to install osTicket, but I just worry that some of the clients will be unable to read e-mail. uvDesk (alternative to osTicket) uses SwiftMail and does not have such issue.

My worry is about some clients won't be able to render non-text/html format in their [probably legacy] e-mail clients. I've read about such stories in the internet, for example here is a complaint about multipart/alternative format can not be rendered in Outlook 2010: https://stackoverflow.com/questions/31502596/php-mail-multipart-mixed-cut-off-outlook-2010.

You know, the problem looks like not too important when some accounter on old PC can not get e-mail, but this is not such fun when this accounter is your accounter :)

Now on the way to understanding how big is the problem...

I would expect a reproducer here before acting then: everything else is just words until then :)

I spent a couple of days working on this. It does turn out to be a bug in laminas\mail\transport\sendmail. Everything is documented in this osTicket bug:

osTicket/osTicket#6305

Let me know if you need more.

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