After installing upd. 60.5.2 MAPI stopped working.
Issue is visible in Explorer window (RightMB on file -> "Send to mail recipient", send file from MS Office 2010, etc.)

IF TB is running, nothing happend after command.
IF TB isn't running, after command "Send......." TB starts main GUI, without "New message" window

In MS Excel after choice "Send as attachment" you obtain error message (translated): "Common mail crash. Close Excel and try again"
In MS Word: "In case of crash the mail system, system failed to send e-mail"

Up to 60.5.0 this function worked well for me, without any problems.

Not a security issue.

In 60.5.0 using "send to mail recipient" crashed TB for me, the 60.5.2 release notes mention this has been resolved, I can confirm it no longer crashes for me, but as per this report, now nothing happens when using "send to mail recipient"

windows 10 64bit, Thunderbird 64 bit (yes I know it's unsupported)

Duplicate bug list:
Bug 1531190 Since update 60.5.2 - Send to > Mail recipient" on Windows no longer works. Windows 7
Bug 1531465 SEND TO MAIL RECEIPIENT STopped work in after update to 60.5.2
Bug 1531352 Sent to mail recipient not working
Bug 1531678 MAPI doesn't work - "Send to mail recipient"

See bug 1530820 comment #30.