Your mail server certificate is invalid error

My case with the "Your Mail Server Certificate is Invalid" error:

New Pixel 2 XL, Verizon carrier, Android 9 (Pie), Outlook mail app (down loaded from Google Play),  while attempting to add a networksolutionsemail.com account.

Here's what I found by pushing every combination of buttons in Outlook for the last several hours (and that only after most of the day fruitlessly Google searching for a solution)

From within the Outlook mail app:

Select Settings

Select Add Account

Select Add an Email

Enter your personal email address and Select Continue

When the screen returns with the Password field, tap the Help "?" (Are you kidding me!? Why the heck hide it behind the "?') where then and only then will a pop up appear to change the Account Provider.

Once Change Provider is selected then the  screen displays the Microsoft, Google, and Other account types incuding IMAP. When you select IMAP then it's back to the account setup screen to enter your password, your name, and name for the account.

However and Moreover, now when selecting Advanced it will display the Incoming and Outgoing IMAP server fields, of which my email account connected just fine when I left them blank.

As a foot note I had also contacted Outlook Support (found them behind the "?"as would be expected) about POP3.

"Thanks for reaching out and I am more than happy to provide information in regards to POP/POP3 accounts. Currently, we do not support POP or POP3 accounts. It is something we may consider adding in the future.

However, POP and POP3 have many limitations, such as the amount of time received mail remains on the server before being deleted and the ability to retrieve sent mail or sync changes in you mailbox on multiple devices.

I appreciate your time and I hope you are having a great day so far!:)"

Signed by my new friend Bob S- Outlook Mobile Support - Android Support / iOS Support (CSS)

Hope this helps.

Outlook doesn't work on Android with major ISPs email.  Used to, but stopped about 2 months ago.  Try to connect, get "your server certificate is invalid".  Many many forum entries. Microsoft are clearly just hoping the problem will go away.  Other Android email clients work fine (I have tried three.  I'm using the gmail app as a workround.)

Same issue here this morning. 

Exchange 2007 with the Mobile Outlook app on both Android and iPhone.

All users reporting the messages as per other recent posts.

OWA working. Certificates all look fine.

This has happened to me, both on the IPhone and IPad with tiscali email, settings have not changed. Microsoft need to sort this out, as it appears a lot of us like using Outlook rather than the mail app from Apple.

****, me too. All my Android users, as of this afternoon, are getting Certificate Invalid, even though it's fine and will be for around 2 more years.

Yes this is happening to all of our sales team as  well. We are using and Exchange server hosted onsite.