EmailSubject Property [Excel 2003 VBA Language Reference]
Returns or sets the text string of the specified hyperlink's e-mail subject line. The subject line is appended to the hyperlink's address. Read/write String.
This property is usually used with e-mail hyperlinks.
The value of this property takes precedence over any e-mail subject line you have specified by using the Address property of the same Hyperlink object.
This example sets the e-mail subject line for the first hyperlink in the first worksheet.
Worksheets(1).Hyperlinks(1).EmailSubject = "Quote Request"