A very odd circumstance has arisen with my mail. With one recipient only, whether I send a message via me.com, or icloud.com or (last resort!) btinternet, from time to time, with no apparent pattern and certainly no logic, some come back with a "failed to deliver" message. I've spoken with the recipient, but they're no help, although they did indicate on the first occasion that they were having some trouble with the me.com addresses. Since this isn't happening except with this one recipient, am I right to assume that the problem must be with them, rather than with me? At present, I'm trusting to luck every time I send them something - they're important for my work, and there's no way around using them. Any suggestions will be very gratefully received.