You can use the match function with a regular expression.
e.g. isMatch($entity/attribute, 'regex expression') this will check if the field contains an email address when using the correct regex.
For email regex expressions have a look at http://www.regular-expressions.info/email.html
There are a number of ways to do this, many of them are covered here: https://docs.mendix.com/howto50/setting-up-data-validation
Comparing a string to a regex for validation in a microflow is discussed in this post: https://forum.mendix.com/link/questions/3133
Also, a recently published widget in the App Store called InputBoxOctober provides this capability (not sure why its named that, but I have used it with good results. You can find this widget here: https://appstore.home.mendix.com/link/app/4625/Mendix/InputBoxOctober
Hope that helps,
This topic has been covered quite a few times on this forum. Personally, I favor Nikel's approach from this thread.