Lot of Mac users faced this issue when sending an email in Mail app on Mac OS X High Sierra, Yosemite, Mavericks, and Mountain Lion. This problem will occur if SMTP server is messed with wrong accounts to use different servers.
Configuring Zoho Mail as an IMAP account in Apple Mail Client. Check if the SSL is turned on for the SMTP server, and that the Outgoing Port Number is right.
Solution 1:-
- Open Mail app.
- Select Preferences.
- In Accounts tab, choose the account which is Outgoing Mail Server (SMTP) labeled as Offline.
- Click the SMTP server and choose Edit SMTP Server List from the list.
- Enter the right username and password.
Solution 2:-
- Quit Mail app.
- Go to Applications > Utilities > Keychain Access and delete all SMTP passwords from keychain.
- Enter the name of your SMTP server in keychain search box like mail.mailserver.com or smtp.mailserver.com.
- Search and find the entry which starts with smtp://. Copy and store the password in your hard drive in the different locations (for safety).
- Delete all relevant password entries for SMTP servers.
- Open Mail app and go to Preferences -> Accounts tab.
- Choose your account SMTP server from Edit SMTP servers list.
- Re-enter the password that you just deleted.
Solution 3:-
- Go to Apple menu -> Force Quit.
- Choose Mail app and select Force Quit.
- Restart your computer.
- Open Mail app and check your issue.
Solution 4:-
Go to Network Preferences -> Advanced section of Ethernet and WiFi interfaces. Add the following DNS addresses.
- 8.8.8.8
- 8.8.4.4
Solution 5:-
- Go to Mail Preferences.
- From the left side list, select the account which causes the issue.
- Choose “Edit SMTP Server List” from the outgoing mail server drop-down menu.
- Correct the username by appending domain name 9Ex: @gmail.com or your own domain).
- Re-enter the password.
If you knew any other solutions for SMTP server offline Mac mail issue, inform us via comments.