Very strange

I'm sitting here scratching my head in puzzlement. Yesterday I called in at the Housing Society office (as I do from time to time) only to find that a reply I had sent to an email from Pat the previous day had not got through and that emails she had sent to me had never reached me. Out of curiosity we tried a few more, with me logged into my ISP on one screen and the Housing Society on another. It seemed that two of my three email addresses (it's a long story) were acting up, but that the third was OK. All of which seems a bit strange as two of the three, including the one that was working, are automatically redirected to the third (the original). But if the original (@brightonlions.freeserve.co.uk) could receive emails addressed to and redirected from @leslavandes.co.uk, why would it not receive emails addressed to itself? And, just to add to my confusion, this morning emails addressed to freeserve are getting through. Well, some of them are...