Broken web page links in emails

Hi all, I have had this issue twice recently, where I have created a link to a [non-Marketo] website page in a Marketo email, tested the sample email OK, and then when the email goes out (which might not be the same day) the link has changed in the Marketo email and no longer works.

Nothing was changed on the email side, and the web page that we want to direct the link to is the same.

Please can you let me know if you have experienced this, and what the problem might be?

thanks

barbara