`Client.Send()` provides the possibility to send multiple `*Msg` in one go. If one of the `*Msg` caused an error with the sending mail server, we were returning completely, while not processing any `*Msg` that came after the failing message.
This PR fixes this behaviour by processing each message first and then return a accumulated error in case any of the `*Msg` processing failed
Additionally, this PR separates the `Client.Send()` method into two different versions. One that makes use of the new `errors.Join()` functionality that is introduced with Go 1.20 and one that handles it the old way for any supported version lower than Go 1.20
- Implemented MAIL FROM RET parameter
- Implemented RCPT TO NOTIFY parameter
Not implemented so far (not sure if we need this at all):
- MAIL FROM ENVID parameter
- RCPT TO ORCPT parameter
TBD:
- Test coverage
# SUMMARY
* Bad licenses:
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* Unused licenses:
* Used licenses: CC0-1.0, MIT
* Read errors: 0
* Files with copyright information: 45 / 45
* Files with license information: 45 / 45
Congratulations! Your project is compliant with version 3.0 of the REUSE Specification :-)