Here’s a quick little post for you on this fantastic, turkey and football-filled Thanksgiving evening!
The Issue
We first noticed the issue in WFFM 8.0 Update-2 (rev.150224) when adding an E-mail field to a form, but as of Update-4 (rev.150625), it’s still an issue.
With this configuration, the e-mail field will fail client-side validation if capital letters are used.
The proper regex string is stored in the /sitecore/system/Modules/Web Forms for Marketers/Settings/Validation/E-mail item, but a bug in the module doesn’t inject it properly.
The Workaround
This is a known issue and Sitecore Support has a patch to correct it. However, in the absence of the support patch, you can also chose to make it a Single-Line Text field and, in the Validation section, select Email Address.
This will inject the proper regex value.
Now, back to your regularly scheduled Thanksgiving activities!
Happy Sitecore trails, my friends!
CitizenSitecore 
I think it’s still broken in Sitecore/WFFM 8.1 Update 2. I think the regex-Aspekt overwrites anything one tries to add in Sitecore.
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After investigating this issue more, it appears that it only effects MVC and it’s still an issue in WFFM 8.2 Update 1
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Hi Jason,
Great post! Just wondering if you came across this issue.
I’ve actually tried using the same method however don’t get any verification on the field when I input an invalid string. Running WFFM 8.1 u3
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