verify signed messages with Outlook

[Rafael]

Hi people,   I’m using a free certificate from Thawte to sign a message with openSSL. In the Linux server that I’m using to sign, I can verify it successfully. But when I send it with the sendmail command The Outlook says that there is an error in the signature, that the content of the message could’ve been altered. Anyone knows why this is happening?   Thanks   Rafael Daraya