c# - Amazon SES Smtp much slower than Raw mails -


why amazon simple emailing service smtp mails 10 times slower raw mails ?

the difference raw mails sent methods provided aws sdk. smtp emails sent using the built in c# code send emails (system.net.mail.smtpclient) points aws smtp end point.

this happens in background service smtp 10 times slower. sending @ rate of 1 per second while our current quota should 14 per second.

could check tcp/ip round trip time between server , "the aws smtp end point"?
use ping or traceroute measure it

sending email on smtp without pipelining requires at least

  • 3 rtt in case of reused smtp connection (mail from:+rcpt to+data).
  • 7 rtt in case of 1 mail per 1 smtp connection (+1 rtt smtp auth)

possible fixes:

  • reuse smtp connection (many messages on single smtp connection)
  • use pipeling (sending commands before receiving pending replies
    email-smtp.us-east-1.amazonaws.com not advertise pipeling support in ehlo reply
  • use few parallel smtp connections

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