Our responses seem to have crossed... > > > I am wrong, but it seams that extending VRFY command is more > > > appropriate for the purpose than using RCPT. > > Hmm. _That_ is an interesting idea, since we have always > > permitted VRFY to do somewhat more poking around in real time > > than one might normally expect of RCPT (where "poking around" > > efforts more often result in a 250 code and an email rejection > > if needed). > If I understand both your comments and Keith's suggestion, the key is a > separate command. > It, too, find that aesthetically preferable. The problem is with efficiency. > A separate command means 2 commands per recipient and it means at least one > synchronization event, between issuance of this new command and issuance of > the first RCPT-TO. You can avoid the need for additional round trips by batching all the capabilities queries with the first RCPT TO. But this results in a rather sharp rise in implementation complexity. > That's quite a bit of overhead, for something that frequently will have no > effect on the content being transferred. Indeed. The average number of recipients for legitimate mail does tend to be quite small, which implies we're optimizing the uncommon case here. Ned