Both are correct, depending on the context.
The Link Purpose (Link Only) guideline states that :
A mechanism is available to allow the purpose of each link to be identified from link text alone, except where the purpose of the link would be ambiguous to users in general. (Level AAA)
So when using a mailto:
URI scheme, you should indicate the purpose of the action within the link. The purpose should be something like "Write an e-mail to John Doe", but you should not forget that the e-mail address itself might be important content which you want to give to your visitors for later use.
For instance, the following links are both correct according to the WCAG.
If you want to insist more on the action than the e-mail address:
<a href="mailto:feedback911212328@example.com">Send feedback to our company</a>
or if you just want to give your e-mail address to your visitors:
Contact me: John Doe, 10 downing street, London,
E-mail: <a href="mailto:johndoe@example.com">johndoe@example.com</a>