I had my Fastmail account incorrectly flagged by their scripts, account fully disabled, bouncing all my emails. It took 5 days for their support to investigate, admit their mistake, reinstate my account and issue an apology (in the form of 1year subscription). Still, 5 days of emails lost.
I triggered their spam algorithm by using the ‘redirect’ button in Apple mail to send an invoice to my administration tool, which keeps the original sender in the ‘from’ field.
I gave them the benefit of the doubt for now, since their offering is really good.
Were you on your own domain? In that situation I guess you could have changed DNS and piped it to Gmail temporarily.
Oh, and one other thing- they disabled my account silently, no notification, no email, call, sms, anything. Found out only when one of my friends called to ask why my address was bouncing emails. As my account was disabled, I could not even easily submit a support ticket as a customer (which requires to be logged in), had to use some contact form on their website.