Troubleshooting Apple Mail
What does Mail/Window/Connection Doctor Show? If the server is red, select it and look at the Show Details box.
Mail: Mail troubleshooting
Mail: If you can’t receive messages.
Mail: If you can’t send messages.
Troubleshooting sending email messages
Mail not sending or receiving messages after updating OS X.
Some other things to try.
Try Mail/Preferences/Accounts /Account Information. Select an account, then go to Outgoing Mail Server (SMTP). From the drop down menu select Edit SMPT server list. Then set up a server for each mail account so that is associated with the e-mail address. Then go to each account and set that server as the Outgoing Mail Server (SMPT). You can click Use only this server if desired.
Mail/Preferences/Composing/Send to messages from - set to account of selected mailbox.
Try Mail/Preferences/Accounts /Account Information. Select an account, then go to Outgoing Mail Server (SMTP). From the drop down menu select Edit SMPT server list. See if the account is listed there. If so, delete the SMTP server for the account. Try to add the Mail account again.
If you are still having problems.
Are you running any anti - virus programs? Using a VPN?
Try setting up another admin user account in System Preferences/Users & Groups to see if the same problem continues. Also try the Safe Mode.
Isolating an issue by using another user account
Safe Mode - About.
If it works in the Safe Mode, try running this program when booted normally and then copy and paste the output in a reply. The program was created by Etresoft, a frequent contributor. Please use copy and paste as screen shots can be hard to read. Click “Share Report” button in the toolbar, select “Copy to Clipboard” and then paste into a reply. This will show what is running on your computer. No personal information is shown. If the log won’t post, try posting it in Pastebin and provide a link in a reply. After pasting the report in a PasteBin page, go to the top of the page, and copy the address in the URL bar. Paste that in a new reply. Pastebin.
Etrecheck – System Information.
Web site version if required. https://etrecheck.com