Microsoft pushes March update, fixing the bug where characters like "/" in classic Outlook for Win10/Win11 turn into question marks

IT Home March 18 News: Tech media BornCity published a blog post yesterday (March 17), reporting that in Microsoft’s latest three versions (2601, 2602, 2603), a BUG has been fixed where special characters in the classic version of Outlook display as question marks.

IT Home previously reported in February that from late January 2026 to early February, IT service providers and ordinary users had gradually reported that after sending emails, the system could not properly recognize certain special characters.

The German umlauts (Umlauts) that previously worked normally suddenly turned into question marks (?) in already-sent emails. Based on observations by some users, this character mutation occurs especially frequently when the recipient uses a Microsoft tenant hosted on servers in the United States.

This BUG affects multiple non-ASCII characters. The symbols Microsoft lists as affected include not only German umlauts, but also the registered trademark symbol (), letters with diacritics (such as é, ü, ) and other extended characters like the pound sign ().

System troubleshooting showed that the garbled-character issue specifically affects the classic version of Outlook 365, with the triggering version being 2601 (build number 19628.20150 and above).

Microsoft formally confirmed the vulnerability on February 6, 2026, and released related technical support documentation. Microsoft ultimately pushed a public update containing a fix patch on March 10, 2026. The Outlook 365 updates that include the fix process are now being rolled out; the first wave of versions integrating the fix patch includes:

Version 2601 (19628.20252)

Version 2602 (19725.20164)

Version 2603 (19822.20032)