How do I increase the maximum allowed attachment size for email sent using msdb.dbo.sp_send_dbmail in Microsoft SQL Server 2005/2008

In the Object Explorer frame of SQL Server Management Studio, expand the “Management” folder. Open the Database Mail configuration wizard.

Click Next-> Choose the radio button for “View of change system parameters” and click Next.

Now change the Maximum File Size (Bytes) property and click Next, then click Finish to save your changes.

See Database Mail Configuration Wizard at MSDN for more info.