The messages from alert.log are not being emailed.
My polling time is 300 seconds.

Some messages are sent through. The majority of sever
messages never make.

Do you get status messages in the DB Alert log (on screen and in db_alert.log) that found messages in the Oracle alert log "to be emailed" to you?

I am trying to undertstand is whether this is an email problem or a message filter problem or something else.

By the way, which DB Tools version are you running?

: The messages from alert.log are not being emailed.
: My polling time is 300 seconds.

: Some messages are sent through. The majority of sever
: messages never make.