Lately, we've had a few clients who have said they weren't getting our emails (replies from osTicket). I didn't see any error message - no mailerdaemon, no mailing errors in the system logs, etc.

I tested this issue by creating a ticket under my personal email. I sent a reply to myself after the ticket was created and it did not come through my email (not spam, junk, etc). The following two replies, however, did show up in my inbox as expected.

I'm on v1.15.1 and on Apache. We're using Dreamhost if that matters.

What other steps should I do to troubleshoot this? I'm not even sure where to look next. It seems really hit or miss and makes it hard to trust that the system is working, which makes me worry that we're missing out on things from our clients and they're missing stuff from us.

You would want to talk to Dream host to have them look at the mailserver logs to see what is happening.
They should be able to trace the message flow on their side.

If the email that you setup is not also hosted with them, you might need to also contact the mail host of the email account to ask them if they are blocking it or something.

Write a Reply...