Hi Magnusnu,
welcome to BwPostman!
Yes, a log file would with these information be helpful. But BwPostman uses the mailer provided by Joomla and from there the only results returned are true or false. At the foreseeable future I have not the time to implement another (own?) mailer to get better return values.
And I see another problem at least with one big German provider: If there come more than x mails from a mail address(, IP or a combination) within y time, all further mails are rejected, nevertheless the recipients are valid or not. You have to register at this provider to be able to send all your mails.
This could be avoided by using a mail supplier like Newsletter2Go, mailChimp or SendGrid. There You surely get the desired information, but this could perhaps create problems with the GDPR, but the support for such platforms also is not yet implemented at BwPostman.
Hth
Romana