This is an archived issue and will only apply to you if you're using OS X 10.5.8
What's the issue?
A security update in OS X 10.5.8 introduced an issue which prevents e-mailing from AccountEdge. This issue only affects e-mail accounts that have signatures attached to them. This happens only on 10.5.8 (Power PC or Intel) with the 10.5.8 security update.
What's the solution?
Turn off signatures in your email account.
To do this:
Go to the Mail menu and choose Preferences.
From the panel on the left, select the applicable account.
From the Choose Signature drop down menu, select None.