One problem that I had with FastMail is that they were bouncing too many messages. I also found that some important-to-me services were being rate-limited from

One problem that I had with FastMail is that they were bouncing too many messages. I also found that some important-to-me services were being rate-limited from sending email for weeks, even though none of the email received was marked as spam (by their filters or explicitly by me). I tried adding the senders to my address book as recommended and nothing changed, I also tried reaching out to support and they took weeks to respond then said "they look spammy". I get that all providers need to do some filtering but if the customer is saying that they want a specific set of emails saying "they look spammy" is not a good response. I ended up picking another provider and closing my trial account.