How many email clients support visibility?

It works in 13 of 21, not supported in 8.

Does visibility work in Apple Mail?

visibility works in Apple Mail. Closest to Fastmail: Apple Mail, which agrees on 192 of the 235 features both are tested on.

visibility in Fastmail

Works visibility works in Fastmail.

Works in 13 of 21 · not supported in 8

Which clients

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

The fix for the clients that need it

Needed in 8 of 21: Gmail, Gmail Android, Gmail iOS and 5 more.

Use conditional comments or remove hidden content

instead

5 lines

<!-- For screen readers, use font-size: 0 trick -->
<div style="font-size: 0; max-height: 0; overflow: hidden;
            mso-hide: all;" aria-hidden="true">
  Preheader text
</div>

Show the original

before

3 lines

<div style="visibility: hidden;">
  Hidden content for screen readers
</div>

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Every feature in Fastmail · visibility in every client

Questions

How many email clients support visibility?: It works in 13 of 21, not supported in 8.
Does visibility work in Apple Mail?: visibility works in Apple Mail. Closest to Fastmail: Apple Mail, which agrees on 192 of the 235 features both are tested on.

To see what in your email Fastmail does not support, paste the whole email.

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Real captures 14 Oct 2026 on 11 installs · caniemail (MIT) via @emailens/engine 0.18.22 · tested upstream 28 Feb 2019 · data last changed 10 Nov 2026 · Outlook (New) cells are the engine's mapping