Outlook 365 - Can't select From email account or set default signature

Greetings,

Specs:
Win 10 Pro x64 - Version 1909 - Build 18363.720
Office 365 / Outlook - Version 2003 - Build 12624.20176, Monthly Channel (Targeted)

Everything was running fine with my O365 Business Premium and its Outlook program on my Win10 PC until this morning when I launched it and encountered two issues.

Issue #1
'From:' email address blank - When creating a new email, the 'From:' email address field is blank, instead of showing my default email account...and I cannot type into the field. And the 'From:' button no longer displays a drop-down of my email accounts to choose from. The button is dead and does nothing now.

• I have several different email accounts setup in Outlook, including my businesses domained email address, some Outlook.com addresses, and some addresses from my ISP. All used to be listed in the From drop-down, until this morning.

Issue #2
Default Email Signatures - While tinkering around trying to solve #1, I noticed in my Outlook options for 'Signatures and Stationary' that all three drop-down boxes for 'Choose default signature' are greyed out and not active, although all my email signatures are listed in the box to the left and can still be edited. In other words, I can no longer choose my default email address. Now, all new emails I start default to my business domained email address.

• Oddly, if within a new email, I select Signature from the Include section of the ribbon bar, I can change the signature to one of my other account signatures.
• I created a new email signature to test if the three boxes would come back to life and they didn't.

I've also done the following:
Run both the Quick and Full repairs for Office365 - Didn't resolve the issues
Restarted O365 in Safe Mode - Issues were present in safe mode

I don't know if the two issues are related, but everything was fine this morning when I closed Outlook. The only thing I did after that was the latest March 12 Win 10 update, KB4551762, then rebooted the PC. A couple hours later, I re-launched Outlook to get to work...and those issues appeared.

I've looked everywhere for a solution, including the forums here, and came up with nothing. I'd really appreciate anyone who knows how to resolve these issues.

Thank you

AndreTen said:

Check with different Windows account. Create a new user, and set up new (I guess .ost file).

If everything is fine there. Your data file somehow became corrupted.

Much depends on your mail provider. guess (again) you have exchange - fastest to set up. Make a backup, delete your account and start over

Yes...they're .ost's on Exchange (except for the ISP's email accounts) and all using IMAP. I just discovered the Microsoft Support and Recovery Assistant for Office 365, which I'm going to give a try. If that doesn't fix things, I'll give your advice a try. Re-setting up all these accounts on Outlook is hairy. Thank you.

- - - Updated - - -

Well...both issues are now resolved. After running the various Outlook repair tools and ScanPST, the issues still existed. But for giggles, I ran Office update...and a new update came in...and presto, both issues were resolved.

So the best I can surmise is that the previous March 12th Win 10 update, KB4551762, broke something that today's Office update fixed. I don't know...just glad Outlook is fixed.