Issue Web browsers (Chrome and Safari) give warnings “This connection is not private” on certain HTTPS websites. After a closer look, it appeared that all affected websites were using Let’s Encrypt certificates. The computer in question was a 2011 MacBook Air running El Capitan Mac OS. The issue was caused by DST Root CA X3 root certificate…

If you are lucky (and if HTML formatting is very simple), you may be able to copy and paste a HTML signature directly into the Apple Mail Signatures box. Just remember to uncheck the “Always match my default message font” box. Unfortunately, if HTML formatting is slightly more complicated, Apple Mail is likely to mess…

Issue Trying to install a fresh copy of macOS High Sierra on a MacBook Air using a bootable USB key. The installation fails to proceed with the following error: This copy of the Install macOS High Sierra application is damaged, and can’t be used to install macOS.

Issue Microsoft Office 365 Exchange account stops working in Apple Mail on macOS. Apple Mail and Internet Accounts in System Preferences prompt to re-enter Microsoft Exchange account password, but after the correct password is entered, just shows spinning wheel icon indefinitely.

Issue Mac OS version of TeamViewer 15 displays the following message in Computers & Contacts tab: You are currently offlinePlease check your internet connection.The application is trying to reconnect The computer is actually online and TeamViewer can connect to clients by manually entering ID and Password. It’s just Computers & Contacts section that doesn’t work.

Issue Time Machine on MacBook Air fails every time with the following error: Time Machine couldn’t complete the backup to “MacBook Air Time Capsule”.An error occurred while copying files. The problemmay be temporary. If the problem persists, use DiskUtility to repair your backup disk. Other MacBooks backup to the same Time Capsule disk with no…

Issue Every time MacBook resumes from sleep following iTunes message is displayed: Your iCloud Music Library session has expired.Your iCloud Music Library session has expired. To reconnect, sign in with your Apple ID and password. After entering correct password the message goes away, but only until MacBook resumes from sleep again.

Issue VLC for Mac stopped showing embedded subtitles. VLC finds the subtitles and allows to enable them, but no actual subtitles are displayed when video plays.

Since Mac OS Sierra Apple added a useful option to automatically remove files from the Trash folder that are older than 30 days. This mostly removes the need to manually empty Trash or use third party tools and scripts.

Issue Opening TextEdit opens a Finder File Picker dialog instead of a blank text document.

I used below procedure to export emails from Office 365 Exchange Online Archive and import them into Mac OS X Apple Mail while doing PST to MBOX format conversion.

If Mac is failing to go to sleep or is waking up unexpectedly, you can run pmset -g log | egrep ‘\b(Sleep|Wake|Start)\s{2,}’ in terminal to inspect last sleep/wake events