So we extend Gitlab::Email::Receiver for this new behaviour, however we might want to split it into another class for better testing it.
Another issue is that, currently it's using this to parse project identifier:
Gitlab::IncomingEmail.key_from_addressWhich is using:
Gitlab.config.incoming_email.addressfor the receiver name. This is probably reply because it's used
for replying to a specific issue. We might want to introduce another
config for this, or just use reply instead of incoming.
I'll prefer to introduce a new config for this, or just change
reply to incoming because it would make sense for replying to
there, too.
The email template used in tests were copied and modified from:
emails/valid_reply.eml which I hope is ok.