How secure is Microsoft Excel 2016 Email Encryption if the file is intercepted

We (My Boss and I) are assessing the security  of Excel password protection for Microsoft Excel 2016 versus complete end to end encryption via something like OpenPGP.  We currently send files via email using Excel workbook (not sheets) encryption.  Can any one please comment on how secure Excel encryption is and the methods of circumventing Excel encryption for the purposes of demonstration for my boss.  I have found links indicating how easy it is to break, are the contributors correct?  - Thanks in advance.

Kind regards,
Andreas HagenAsked:
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No, those links are not correct - please share them.

wikipedia's info on office encryption:

Microsoft Office password protection is a security feature to protect Microsoft Office (Word, Excel, PowerPoint) documents with a user-provided password. As of Office 2007, this uses strong encryption; earlier versions used weaker systems and are not considered secure.

The 128-bit key AES protection employed in newer Office 2007–2010 remains secure. In fact, the RC5 project has been trying to brute force an RC5 72-bit key since 2002, and as of 2013 has not successfully done so.[1] Furthermore, even utilizing all known breaks (that speed up brute force attacks by a factor of about four) it would take a typical computer millions of years or longer to break a 128-bit AES key of sufficient length and complexity.

The 40-bit key RC4 protection used in earlier versions of Office, 97–2003, can typically be bypassed with password hacking software.

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Jan Karel PieterseExcel and VBA ExpertCommented:
It depends on how exactly you protect the Excel file. Worksheet protection is very simple to break, a password required to open the file is very hard to break.
Andreas, could you please return and close this question?
@broomee9: there is not much more to be added but "password protection is strong" and that was said and supported by wikipedia's info.

Why did you decide this is no solution?
I object, since I think it very well serves as a solution.
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