On Apple Discussions Martin Marconcini has discovered a way to bring Mail.app to a screaming halt in three easy steps.

Frustrated by Mail’s tendency to freeze when he dragged anything onto Mail’s Dock icon, he went back and painstakingly restored his Mail installation step-by-step until the glitch re-emerged.

Here’s what he discovered (you can test it for yourself):

One: Set Mail’s New message default in the Composing preference pane to plain text.

Two: Add a signature to your email account in the Signatures Preference pane. Make sure that you select it at the bottom of the signature pane to be added to every new message by default:

Three: Drag an image or anything else onto Mail’s Dock icon.

That’s a big, 100%-repeatable train wreck for me.

It seems like a common configuration; it’s not restricted to dragging ClarisWorks documents onto the Dock icon when the signature contains a particular accented Laotian character. How does such a thing not emerge in internal testing? Perhaps I am too romantic about internal testing.

Anyway, happily, I am in the clear. All my signatures are just a few keystrokes away in TextExpander.

But Martin suggests some workarounds for those plagued by these freezes:

a) Use Rich Text (not an option if you use Blackberry or need plain text)
b) Use Plain Text but remove the signatures (can be a Pain In the A** if you use different business accounts like me with odd disclaimers that are a “must”).
c) Roll back to Safari 3.0.* and either use it or use Camino/Opera/Firefox/Etc. Could be a problem if you rely on Safari stuff like Inquisitor, 1Password, etc.
d) Don’t drag attachments to the dock icon…

On 8 April Apple acknowledged this as “a known issue, which is currently being investigated by engineering”.