As subject reads, during the email config and test, I receive the test email fine. The email server is at 1and1.com and I can receive email on a 1and1 account and a Gmail account. When I do a test order to trigger a confirmation email, I don't receive an email and this shows in the error log:
Service not available, closing transmission channel. The server response was: dns lookup failed for sender domain
I've tried using both the domain name and the IP address for the configuration and it results in the same error.