EHLO likely didn’t fail; postfix is saying that the sending end sent an EHLO and then dropped the connection. Something like this:
[baron ~]$ telnet forum.tasat.org 25
Trying 64.176.213.39...
Connected to forum.tasat.org.
Escape character is '^]'.
220 ESMTP server
EHLO baron
250-forum-mail-receiver.localdomain
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250-DSN
250 CHUNKING
^]
telnet> quit
(you’ll probably see a similar message in your logs referencing my IP)
This is a problem on SES’s end. I’d advise watching the traffic coming in on port 25 to see if there’s any indication why it dropped, or check SES to see if it has any logs.