mailto: Specifying Multiple Recipients

Up until about 20 minutes ago I was unaware you could specify multiple recipients in a mailto tag:

<a href=','>Email Us</a>

(Tested in Firefox, IE6, Outlook 2003 and Thunderbird on Windows)

Activating this link will open up the users default email client and pre-populate the to: fields with the multiple addresses.

But (isn’t there always a but?), there is an upper limit on the number of people you can address.

I’m not sure what the upper limit is, but 539 (the current size of my test data) is too much. Activating the link does nothing.

I’m not sure if this is a problem with the mailto: tag, the browser or the email client.

More info as I explore further…


(unconfirmed) Looks like there might be a maximum length for a href attribute of around 250 characters)


Software developer by day, scale model builder and wargamer by night.

Posted in XHTML & HTML
13 comments on “mailto: Specifying Multiple Recipients
  1. VxJasonxV says:

    The character limit is probably listed in w3 spec’s, or an RFC somewhere.

  2. Jason, I did spent about 30 mins digging around the docs and various google searches. I didn’t come up with any exact numbers but I did find a reference to the largest mailto: attribute string (250) and extrapolated from there.

    I think that’s the first time I’ve ever used the word extrapolated.

  3. Lifeng Zhang says:

    Hey there, I’m currently working on a website where we’ve hit this problem. We have too many addresses in a mailto link, and clicking it doesnt do anything. Have you found a way around it?

    I’ve done a bunch of googling and turned up empty on this issue. I couldn”t find mention of a limit on href string lengths or anything

  4. Sorry to disappoint Lifeng, but this isn’t a viable way to email a lot of people. For that you’ll need some server side code.

    PHP (for example) has a built in mail() function ( ) which has no problems emailing large numbers of addresses.

  5. Stephen says:

    I’ve heard tell that there is some sort of registry fix out there that will conquer that 250 character limit. Still searching for it however.

  6. You can’t rely on the fact that your potential users have tweaked their registry though 😦

  7. Steve Hollasch says:

    Regarding Outlook, this depends on each Outlook user to have selected the option to allow commas as address separators. Won’t work for me, for example, as I don’t have this option enabled.

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  9. Pedro says:

    This site suggests using an alias as your main recipient in the mailto link, and then having that alias configured to point to any number of other addresses. Nice and clean, doesn’t require any server-side programming, just a tweak to your mail server settings.

  10. Hi!
    The separator should be a comma (,) and there should not be a space. – documentation

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  13. Joe Boniface says:

    Noticed that using single quotes instead of double quotes around the ‘mailto:….’ parameter made all the difference when specifying multiple addresses separated by commas and having no spaces between addresses. Works with singles, not doubles.

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