Mail stopped connecting to email accounts

[Big Stevie]

Any suggestions please why my Mail is suddenly not connecting to the email accounts I have always used - hotmail.com, hotmail.co.uk & gmail? I get the warning triangles as shown in the image below...

However if I log into Outlook and Gmail websites the email accounts are fully working. Last night they suddenly all came back online, but this morning they aren't connecting again. Noticed I can't Airdrop from my iPhone to my Mac either, is this related?

When I go into Preferences for each account they are all showing as 'on line'..

 

[BrianBaughn]

Off the top of my head…things that might cause that:

Using a VPN
DNS server(s) not working properly
A Mail extension not working properly
Email server(s) not happy with macOS Mail privacy settings

 

[Big Stevie]

Today the two hotmail accounts have now connected and working fine again, but not my gmail or iCloud accounts. Strange behaviour.