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Can’t send Outlook email? The fix has arrived, at last

Microsoft has finally released a fix for what can only be described as an ‘unforced error’ or bug in Outlook that stopped some messages going out. They’ve left an unanswered mystery.

The problem started after an early 2021 public update to Outlook 365 for Windows.  Some messages refused to be sent out with only this unhelpful error message “Cannot send this item”.

The unhelpful error message. Source: Microsoft

No details, no error code and no clue to what the problem might be.  In other words, nothing that could help either the customer or Microsoft identify the problem.

The bug was first reported in early February 2021 but the fix took over two months to work its way through Microsoft bureaucracy.

The result was the usual confusion and delays while customers wasted time and money on the problem.  Meantime not being sure if anyone relevant at Microsoft knew about the bug and was working to fix it.

What was the problem?

The bug was in the SafeLinks feature which checks all hyperlinks in emails and warns if any are suspicious or dangerous.

SafeLinks ‘wigged out’ when the reply has:

  • a long link.  Microsoft doesn’t say what they consider ‘long’.


  • the 2,084th character in the link is an escape character.

The second possibility is very obscure and presumably very rare.

The first bug trigger seems a lot more likely.

Microsoft is not saying how long a link causes the bug.  That’s important for customers to know, especially if they have to edit a message to work around the bug.

Without that detail, customers waste time removing or editing links they don’t need to.

The mystery makes us wonder if embarrassingly short links are involved and Microsoft is trying to save face?

The fix

The late April 2021 update to the public ‘Current Channel’ release includes the Outlook 365/SafeLinks bug fix.  Build 13913.10000 or later.

Enterprise users / admins have the option of switching to the Semi-Annual Channel which didn’t get the bug.


If updating or changing channels aren’t possible, here’s other workarounds.

  • Change the message format from the usual HTML to Rich Text format.
    Microsoft says to use Rich Text but plain text might also be an option.


  • Remove any long links from the message body.  Again, what’s a ‘long’ link in this context?
    Microsoft says to ‘remove’ the link – if that’s not practical, break the link into two or more segments separated into lines that the receiver has to re-join.


  • Send via the Outlook Web App/Access OWA in a web browser

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