Dave Crocker writes: > On 7/21/2025 3:26 AM, Barry Leiba wrote: > > The number of message recipients is > > unrelated to the number of RCPT commands for the purpose of this > > discussion, and the fact that messages often have many recipients does > > not mean that MSAs and/or MTAs need to use multiple RCPT commands in > > one SMTP transaction.
The number of recipients and number of RCPT commands are DEFINATELY related. The number of RCPT commands will normally be either same or smaller than the number of recipients unless one the addresses is mailing list. I.e., to be able to have multiple RCPT commands you do also need to have multiple recipients, and those recipients need to be in the same SMTP server or at least share the same next hop SMTP server. As I said in the enterprise uses it seems to be really common to CC lots of people inside the company to almost all email threads, and depending on those environments there might be a lots of email recipients going to the same next smtp host allowing the MTA to issue multiple RCPT commands instead of sending emails as separate SMTP transactions. Quite often in those environments the initial hop going out from the company is some kind of middle box that does all kind of things to the email, for example adding warnings that this email is confidential, or virus checking etc, and it would be beneficial for it to be able to do those operations for every single recipient at the same time, i.e., IT adminstrators in those environments will most likely try to make so that emails are sent using one SMTP transaction with multiple SMTP recipients. > The earlier, extended discussion about this had various postings about > average number of recipients listed in the RCPT-To command of an SMTP > session. The average number was barely larger than 1.0. There are systems that will always split emails to separate smtp sessions, and that will lower the average, but as I said in my previous email I did see about 2-3% of emails going through iki.fi having more one smtp recipient in one smtp session. > That is, the /observabl/e number of recipient addresses in nearly all > SMTP sessions was essentially 1. Nearly all = 97% of time in internet in general. I would assume it is much bigger if you take same statistics inside the enterprice system that does not explictly split each emails to separate transactions. -- [email protected] _______________________________________________ Ietf-dkim mailing list -- [email protected] To unsubscribe send an email to [email protected]
