550 relay not permitted?

If you are in the USA, as indicated, it is hardly surprising that a message from you to you, directed through what appears to be a UK-based mail server, would say relay not permitted.

Mail servers have the capability of accepting mail from any source for delivery to any destination. If the source and destination are not "local" (from the mailserver's perspective) this is called relaying. To help control spam most mailservers have relaying turned off, and so will only accept either non-local mail for local delivery, or local mail for local and non-local delivery.

Local is determined, in general, by the domain name. So itcarlow.ie mailserver will accept mail from me to one of my colleagues, and will accept mail from me to you, and will accept mail from you to me, but will not accept mail from you to you.

Sorry if you know all that already. The question that remains is, why is your mail being routed through that mailserver? Try sending me a mail (address is in my profile) and I will see if I can glean anything from the headers.

AK

The problem seems to have been caused by a typing error in the To: address, so comcast became comast. Since comast.net exists the message was delivered to its mailserver, uk2mxarray3.uk2.net. The wording of the error message (relay not permitted) was not helpful, as 550 is also the error when the target user does not exist, as is the case here.

AK