Your screenshot does show an imbalance of 'EHLO' (14) and 'QUIT' : which mark the start and end of a normal SMTP conversation.
What your screenshot doesn't show is whether some of the sessions failed (for whatever reason) - can you first confirm that no exceptions were thrown between the 'EHLO' commands and the subsequent 'QUIT' commands ?
Once you have confirmed that there really is a 2:1 ratio of SMTP session (do you see a build of SMTP sessions on your email server as well : is there a way of checking?) : I think you will need to log an SR to get more information - debugging the EmailListener can be tricky and you will likely have to ship logs back and forth.
On the other hand - if you don't mind sharing the logs over the forum; (if this is from a test system etc.) - then please attach a representative sample - that we can take a look at and work with you on.