A friend sent me an email which bounced back to her with this message: Undeliverable.......5.1.0 - Unknown address error 550-'(result of an earlier callout reused).' The address she'd sent it to was correct. What does "result of an earlier callout reused" mean? She's a newbie and we're exchanging emails just so that she gets daily practice; if she's doing something odd I'd like to sort it out sooner rather than later. She's with Talktalk.
thanks, everyone; but none of the links - or your suggestions - offers an explanation that fits. My friend and I have exchanged emails over the last 4 or 5 days without any problems. No, she isn't blacklisted or blocked at my end - I checked that,(in fact she is on my "friends" list). And it surely wasn't the content - we were discussing the weather!