re :come back to your computer, and don't even know the email has arrived. Some suggestions:

Do you have the option turned on to 'Show a tray icon' ? If yes, then when you come back to computer you would see an envelope in the tray and instantly know you had new mail.

If you had the 'Show an alert' also selected, when you click on envelope in tray it would pop up showing summary of what had arrived.

If you had seleted to use a sound file and you can choose one you prefer which is a bit more lengthy or more obvious than a beep, this would also get triggered, but you would also need to seriously turn up the computer sound.

All mail account names which receive new unread mail will turn into blue bold coloured font if new mail has arrived since you checked that account. So this is an immediate indictor of new mail.

Do new unread emails show in bold font? You can also use the 'Quick Filter bar' to show only new mail in the selected folder. This view makes it easy to quickly see what is unread.

If you are looking for emails from specific email address: You could set up a folder for them and then create a Message Filter which auto puts those emails in that folder, so you know instantly where to check for those specific emails.

Hello Toad-Hall

I finally found an add on that does the trick (Mailbox Alert). Using it as a filter, it lets me use another sound and notification which remains visible for as long as I want.

Thanks SafeTex