[Info-vax] SMTP chunk sizes

[Stephen Hoffman]

On 2015-03-20 16:36:22 +0000, Rich Jordan said:

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

That's the easiest way to deal with this, at least in the short term.   
Gateway (relay) through Postfix or some other mail server.  Adjust your 
SPF if needed, if you're using that.

What the Microsoft folks are referring to is ESMTP (EHLO and all), a 
barrage of RFCs that have been around since ~1995.  AFAIK, VMS with 
TCP/IP Services knows not of ESMTP, which means no transport-level 
security, no chunking, no authenticated SMTP, no UTF-8, etc.   You 
could ask for this enhancement from HP, but I'd suspect it'd only be 
VSI that might eventually provide it.   This unless somebody ports over 
OpenSMTPD or some similar software, or gets the Lamson Python mail 
server working.  There's also the potential to switch over to one of 
the Process IP stacks.

There are obviously document-size limits with most mail servers, so 
there's inevitably a transfer size limit here somewhere.  Some folks 
use one-time links or other non-SMTP transfer mechanisms, and some 
clients such as Apple Mail.app with "Maildrop" automate this process.


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