Email address format is not documented and not intuitive

[RincewindsHat]

Describe the bug

Recipients (email addresses) have to be given comman separated, but this isn't mentioned anywhere at all.
If someone would naively assume, that the format is one address per line, this silently fails and no reports are
received at all.

To Reproduce

Steps to reproduce the behavior:

1. Add

emailA@example.com
emailB@example.com

to the recipient list
2. Don't receive any reports at all

Expected behavior

Email addresses get separated by , AND whitespace characters

OR

A tooltip tells one how to insert addresses and warns if the format is wrong