View Single Post
Old 9 Feb 2019, 08:35 AM   #4
n5bb
Intergalactic Postmaster
 
Join Date: May 2004
Location: Irving, Texas
Posts: 8,917
Quote:
Originally Posted by gj15 View Post
This could be symptomatic of your IP address having a reverse DNS problem, discussed towards the end of this thread: http://www.emaildiscussions.com/showthread.php?t=72258
That’s a good possibility. The Fastmail SMTP server has to do several things before the SMTP transactions used to send a message begin:
  • The preferred server is smtp.fastmail.com over port 465 (SSL/TLS must be activated, but not STARTTLS). The client and server must negotiate the SSL/TLS connection, but usually this is very fast.
  • The client IP address must be accepted. There are block lists for known insecure IP addresses.
  • If the IP looks suspicious (such as not resolving to a reverse DNS), the connection can be greylisted. This will defer the connection with a delay. The client will retry and eventually get connected.
  • Authentication using an application password must be completed.
  • The SMTP server reports that it is ready to accept commands. This is where the email transfer occurs.
Bill
n5bb is online now   Reply With Quote