[Info-vax] SMTP chunk sizes

[Rich Jordan]

We have run into a problem with the sites using VMS as a mail server.  Even the current V5.7 eco 5 (or 4) are having problems sending large emails to recipients on microsoft Office 365.  So far other services are not so affected.

The issue seems to be that Office 365 is both very slow acknowledging a received SMTP record (one line of the file, text ot uuencoded) at 250-300ms (per our firewall running packet traces), and enforces a 10 minute connection lifetime for any inbound SMTP connection.

They state the problem is the VMS MTA doesn't provide the (I believe RFC optional) chunk size options and start sending the data in larger chunks.  If it did then the very slow ACK times would not matter.  So the current situation takes many minutes to send a 6-8MB file and somewhere in that range, takes too long to send and Office 365 sends a 421 error and drops the connection.  The VMS MTA does not log the 421 error (we see it in the packet trace but not in even full debug SMTP logs); it just shows the connection timing out.

Messages sent to GMAIL and other sites are still kind of slow but the ACK responses are much faster (<100ms max, usually faster) and there's no timeout.

MS says this is a design decision and not subject to change, so as of now the client can no longer send larger docs to Office 365 recipients.

I reviewed the docs and release notes but didn't see any mention of support for the SMTP chunk sizes; doesn't mean its not there but undocumented.  Is anyone aware of support for that in any version of TCPIP services?

Currently setting up another box to act as a smarthost...

Thanks

Rich