doug, you second suggestion - re: the article at http://sendpress.com/support/knowledgebase/troubleshooting-sending-email/,
i had already read that before writing to this forum. there are 3 suggestions:
the first is try using Send Test Email, which i had already done immediately on discovering my sending problem, and got exactly the same dialog (Debug Info) saying the 3 ports were blocked and the mail could not be instantiated.
the second suggestion starts off "If all the appropriate ports are open ..." so does not fit my case. the third is about spam folders - and i'm not that much of a novice! also, in my case, the mail does not leave the send queue at all.
p.s. the only reason i tried port 2525 was after trawling around on forums for several days, and finding a blocked port 25 problem dating back a few years, where it was suggested to use 2525 because some ISPs block 25. obviously it's pointless for me to try 465 and 567 as they are blocked too.