Open-source is good for solo and small projects, but there are commercial solutions with continuous support, etc. and other features (e.g. SMS) like Mailosaur too
Somewhat related anecdote. Whilst we didn't get cut off, we found a huge drop-off in time to receive, and the quality of, support from our live chat/support messaging provider.
Having been a customer since our launch [1], and very early after theirs, it has been really sad and frustrating to see that friendly distrupter energy zap out of the service.
I get why businesses go through that changes like this during growth, but it feels like all the things to let slide, your persona is not one of them!
[1] https://mailosaur.com (somewhat related to the thread we let you test SMS messages)
[0] https://mailosaur.com