eventout emails are backing up causing delays in ticket email notificaitons

We have an issue that started Monday. we monitor the eventout table for evtype email. When we have more than 3000 records in the table, we get paged. This started Monday.

Every day this week, at about 10:00 am, the email outbound just starts to back up, and emails are delayed by hours. Right now, there are over 15,000 email records in the eventout table waiting to process, and the delay is currently at 3.5 hours. I'm not sure how to improve this or what may have caused it. I really doubt our ticket volume increased that much all of a sudden. These emails are mostly notifications to members of the assignment groups that new tickets were assigned/reassigned to their groups, or possibly notifications of SLA future breaches (also to members of the assignment group).

I'm not 100% sure what all the pieces are that process email.

we start the process in the sm.cfg file with the command: sm -emailout -clean
This starts a process in the status screen called EMAILOUT that uses SCAuto. This process seems to start every 60 seconds.

There is also the event background process. This also seems to start every 60 seconds.
The info record shows the following for event in the startup record:

RAD Application: scheduler
Class: event
Wakeup Interval: 60
Priority: 1

The emails are piling up. When the process wakes up, it seems to only do a very small selection of records, then it goes back to idle for another minute. For example, I have now over 16,000 email records in the queue, the oldest is 3.5 hours old. the last time I refreshed several times to clear the records that were processed, only about a minute (Evexpire time) of records had been removed (ie: oldest was today at 12:37:29. I refresh until it goes idle again, and now the oldest record is 12:38:33. I can keep refreshing, but because it's gone idle, no records will be removed for another minute.

Why doesnt it process all current records at a time? it's appears to be doing maybe 100 at a time, but I cant tell, as the new emails are coming in faster than the old ones go out.

We are on a Unix system.  The parameters from our sm.ini file are:

# Email Out parameters

any guidance on troubleshooting this, or how to improve the efficiency?