[Info-vax] SMTP chunk sizes

[JF Mezei]

On 15-03-20 12:36, Rich Jordan wrote:

> 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)

If you are talking about data being sent after having send the DATA
command and before the ending ".", SMTP does not acknowledge lines of text.

To my knowledge, VMS doesn't support the BDAT extentions (not even sure
it supports EHLO).  This involves using the BDAT command followed by
number of data bytes that follow. This eliminates the need for the
receiver to scan for the CR-LF . CR-LF (dot alon on line) as terminator
for the DATA phase).

https://tools.ietf.org/html/rfc1830

But if VMS uses just the DATA command, it just sends the message data as
PACKETS (and one packet can contain up to 1460 bytes, or 18 lines of 80
characters).

ACKs are done on a per-packet basis, not in a per-line. And there is a
windowsize that is dynamically calculated and adjusted which tells the
sender how much data can be in the pipe (data sent, but for which an ACK
has not been received).

With a DATA exchange, there is just the wait for the OK to enter DATA
phase, and the OK after you did the .<CR><LF> to confirm receipt of
message. (this is where modern mail systems would reject spam messages
based on content and tell sender message was rejected).


There are SMTP debugging logicals you can enable
(some are documented at:
http://www.vaxination.ca/vms/tcpip_smtp_systartup.com

which will give you the full dialogue between the VMS sender and the
Windows receiver. Not sure it has time, but you will at least see what
SMTP commands are used.