[upchuck]

I manage hundreds of contacts via email lists to serve multiple projects for my nonprofit

Consider Vertical Response (free) or Revolution By Email ($30/year).

[Utilizer]

https://www.fastmail.fm/

Works well. Plus, using Opera’s email function I can set Opera up to check the email account(s) automatically and then read them without having to actually login to the email site unless I need to respond to an email or delete spam.

Opera also pops up a temporary little notice to let you know when a new message has arrived. Handy.