Limiting any Email app via FireWall to improve its privacy

The subject applies to any email client on any operation system except eOS, where everything is transparent enough. Personally, I came to this point after I realized what a pain it is to find any good email app on macOS that would be open-source and give you confidence in its privacy. And then I thought: wouldn’t it be easier to take whatever most convenient and just limit it from calling home?

As we know, email communication needs only a few protocols to work, and probably all that needs to be done is to block all ports for selected application except the following ones:

IMAP: 143, 993
POP: 110, 995, 1109
SMTP: 25, 465, 587
LDAP: 389, 636, 3268, 3269

But I’m not an expert, so I’d like to ask you guys: is it correct and will it work at all?

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