Happy with Fastmail here as well - but if you're using your own domain name & are concerned about being flagged as spam, make sure you read up on how to add SPF and DKIM records into your domain DNS records. It's pretty much essential now for functional email. SPF & DKIM are basically a list of IP addresses you authorize to send mail in your name, and a public key for authenticating/signing your emails. Since you're here on HN, setting those up is definitely something you'll be able to understand & do.

The interesting side effect of having SPF/DKIM setup is I can receive reports from Google & other mail providers when someone tries to send spam spoofing my domain name. Seems that China Unicom & ChinaNet are running an enormous botnet that continually sends phishing attacks to Japanese Amazon users, while using my domains in the From field.