When sending an e-mail to someone, the name of which includes a dot ("."), the SMTP protocol requires that the name is surrounded by quotes. Unfortunately claws-mail doesn't do that, and while most e-mail servers will accept the mail and add the missing quotes themselves transparently, some servers aren't that friendly and will either reject or drop the e-mail. Can claws-mail please add the missing quotes around recipient names as needed?
As far as I can see, the problem was not yet addressed as of version 3.7.5.
I am now running version 3.7.10, and the problem is still present.
Duplication it's the other way round, but anyway it's fixed now ;) *** This bug has been marked as a duplicate of bug 2210 ***