How many email clients support ?

It works in 10 of 21, partial in 4, not supported in 7.

Does work in Apple Mail?

works in Apple Mail. Closest to Proton Mail: Apple Mail, which agrees on 203 of the 300 features both are tested on.

<form> in Proton Mail

Not supported <form> is not supported in Proton Mail.

Works in 10 of 21 · partial in 4 · not supported in 7

Which clients

Works: Gmail, Gmail Android, Outlook iOS, Outlook Android, Apple Mail, Apple Mail iOS, Yahoo Mail Android, Samsung Mail, Thunderbird, AOL Mail
Partial: Gmail iOS, Outlook 365, Outlook (New), Outlook for Mac
Not supported: Outlook Classic, Yahoo Mail, Yahoo Mail iOS, HEY Mail, Proton Mail, Fastmail, Superhuman

Your reader in Proton Mail sees the email without <form>, even if it looks right where you tested it.

The fix for Proton Mail

Replace embedded form with a link to a hosted form

The engine still flags this in the fix: Proton Mail does not support "text-decoration".

after

13 lines

<table role="presentation" cellpadding="0" cellspacing="0">
  <tr>
    <td style="background-color: #6d28d9; border-radius: 6px;
               padding: 12px 32px;">
      <a href="https://example.com/subscribe"
        style="color: #fff; text-decoration: none;
               font-family: Arial, sans-serif;
               font-weight: bold;">
        Subscribe Now
      </a>
    </td>
  </tr>
</table>

Show the original

before

4 lines

<form action="/subscribe" method="POST">
  <input type="email" placeholder="Email" />
  <button type="submit">Subscribe</button>
</form>

Test this fix, free

Proton Mail opens with a free account; the checker shows five clients without one.

The checker needs a computer screen.

A free account opens all 21 clients and keeps your checks for 7 days. Create a free account →

What Proton Mail does with <form>

@emailens/engine 0.18.22 on the original code

Proton Mail strips form elements.

caniemail record, tested upstream 10 Sep 2019

Not supported. The <form> and its entire content is removed.

Your next question

Every feature in Proton Mail · <form> in every client

Questions

How many email clients support <form>?: It works in 10 of 21, partial in 4, not supported in 7.
What do I use instead of <form> in Proton Mail?: Replace embedded form with a link to a hosted form.
Does <form> work in Apple Mail?: <form> works in Apple Mail. Closest to Proton Mail: Apple Mail, which agrees on 203 of the 300 features both are tested on.

To see what else in your email Proton Mail does not support, paste the whole email.

Check your email, free

No signup · Five clients free, Outlook Classic included · All 21 with an account

The checker needs a computer screen.

caniemail (MIT) via @emailens/engine 0.18.22 · tested upstream 10 Sep 2019 · data last changed 10 Nov 2026 · Outlook (New) cells are the engine's mapping