Is it possible to modify "from" field in mailto link?

I'm trying to get a mailto link that would open a new outlook email window with a modified from field (i.e. to use a secondary account as it were). Is that possible?

No. Certainly not in most of the popular mail clients.

I assume you are wanting to do this just to save time in your own mail client. I would certainly be annoyed with a website that tried to change my from or reply-to address, so I'd expect my mail client to ignore it.

MAILTO is designed to facilitate a sender contacting an address that has been listed on a website. So there are very few things that the sender would expect to have dictated by the website. Even the standard options can be pretty annoying if handled badly by the website owner.

Your options are pretty much limited to

• subject
• body
• cc
• bcc

Even if a client were to support From (and I am not aware of any that do), there is no obvious way for them to handle edge-case scenarios such as a from address that has not been configured in the mail client.

What do you need this for? Perhaps you can use a script to send mails and dynamically set the From header. For example, PHP has a mail() function which would allow you to set a custom From address (and modify other headers).