MS Outlook 2007 SP3 having intermittent problem - stuck in Outbox

MS Outlook 2007 SP3 having intermittent problem sending e-mail.  1&1 is the host, and the e-mail is the generic info@ catchall for the business.  3 computers are configured for that e-mail (2 Windows 7, 1 Windows 10).  The Windows 10 replaced an a third Windows 7 which had the exact same problem for the last several months.  The Windows 10 is new and has the same problem.  The other old Windows 7 computers have never had the problem.  All computers are running Outlook 2007 SP3.  Currently they all have the same settings for SMTP.  1&1 gave me a different SMTP server to try, but no difference.  Outlook is using a PST file, which I imported calendar and contacts from the computer that had the problem (W7).  The fix is to close Outlook, and run CCleaner, and then reopen Outlook and it works every time.  This was the same on the W7 problem PC.
Jason JohanknechtIT ManagerAsked:
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bbaoIT ConsultantCommented:
can i first know what's the email provider or hosting services provider?
Jason JohanknechtIT ManagerAuthor Commented:
1&1 as I stated above.
bbaoIT ConsultantCommented:
>  The Windows 10 replaced an a third Windows 7 which had the exact same problem

do you mean the problem W10 was directly upgraded from the W7 already had the same problem, not a re-installation from the scratch. correct?
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Jason JohanknechtIT ManagerAuthor Commented:
The Windows 10 PC is a new PC.  Physically no relation to the third PC mentioned.
bbaoIT ConsultantCommented:
okay, what's the SMTP settings of Outlook 2007 for the new Windows 10 PC?
Jason JohanknechtIT ManagerAuthor Commented:
They have 2 options for SMTP:

Port (for SSL Encryption)      465
Port (TLS/STARTTLS, alternative to SSL)      587
bbaoIT ConsultantCommented:
why two SMTP host names and ports? for two email accounts?
Jason JohanknechtIT ManagerAuthor Commented:
Those are the options for 1 e-mail.  I have tested them all, and the problem is the same.
Davis McCarnOwnerCommented:
If 1and1 supports using port 25 (the default for SMTP) have you tried that?
Numerous ISP's used to block port 25; but, many now block port 587.  I have had to change several clients from 587 to 25.
Bud DurlandDirector of ITCommented:
What does CCleaner report having cleaned?  What is it changing that makes things work?  Have you tried using a different, SUPPORTED e-mail client, such as eMClient?  Is there and SSL related patch for OutLook that you have not installed?
Sudeep SharmaTechnical DesignerCommented:
I would agree with Bud, please check if you have Windows update or Office patch which is not yet installed.

Then check the logs from CCleaner and help us to know what is it doing to make the Outlook work.

Jason JohanknechtIT ManagerAuthor Commented:
All Office patches available have been applied.  Temp files in CCleaner.  Remember, that the issue is intermittent.  Outlook 2007 works most of the time.  Office 2019 is going to be deployed in the next couple of weeks.  Will report after that.
Jason JohanknechtIT ManagerAuthor Commented:
Computer is upgraded to Office 2019.  So far so good.
Jason JohanknechtIT ManagerAuthor Commented:
Office 2019 resolved the problem.

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