Problem after updating to 10 8 5
If the only issue you are experiencing pertains to sending email out of Mail app, then try these two tricks to fix SMTP sending errors in Mail for OS X, that fix continues to work in this situation.
On the other hand, if you’re having login errors and problems checking for new email as well as sending, we have another solution which many users report to be successful.
Tip: There is another way to restart network adapter, Click on notification icon at bottom right corner and click on Flight mode to turn it on and off. Troubleshooting your network adapter may also help some cases.
So, use the Windows troubleshooter feature to troubleshoot and fix your wireless adapter to get over this problem.
You might also want to know about the April 2019 Windows 10 update or how to Opt-Out Windows 10 Preview Updates If you get stuck on this problem too, then try the following methods which I have done to resolve the issue.
You might need to reinstall other networking software afterwards, such as VPN client’s software or virtual switches.
Again with a new i OS update - i OS 12/13, a lot of people start getting stuck with issues or minor bugs which makes them unable to complete the installations of the newest update.
There are users who have found themselves in a problem where they get a messages saying "Unable to Install Update, an error occurred installing i OS 12/13".
That should resolve whatever Mail problems have occurred in OS X after installing OS X 10.10.4 or OS X 10.11 El Capitan, but if you continue to encounter trouble, specifically with SMTP mail accounts, these solutions should do the trick.
Not all users encounter this issue with Mail app after installing an OS X update, and though the reason is unclear, it’s possible the problematic setups had configured an email account some time ago, and could be using legacy settings for a specific mail server.