Outlook emails do not get delivered

Good day. I am using microsoft outlook 2007 on windows 7 , 64bit.
My email account is setup correct according to my service provider (in coming and outgoing settings).
POP3 account.
When I do a "test account settings" it shows as successful.
When I send an email, it shows "send/receive complete" with no error message.
The email goes out and does not get stuck in the outbox.
PROBLEM - emails do not get delivered to the recipient.
I do receive emails.
When I use Roundcube, my e mails get delivered so this is definitely not a server problem but a problem on Microsoft Outlook.
WEIRD - when I send an email from another account to the problem account and I ask for a read receipt and reply from the problem account, the read receipt sends and get delivered from the test account.
I have 3 accounts on my laptop and I have this problem on all 3 accounts
Everything was working fine till this morning. Nothing new installed, nothing changed on laptop.
Also re-installed Office. No success.
ANY HELP PLEASE!!!!!!
Thank you for your time.
H
 
What antivirus do you have installed AND is it scanning outging email.
 
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