Sendmail FAX configuration

I've been trying to send FAXs from an HP_UX server using sendmail via an Esker FAX server. However if I try to include FAX configuration details in the receipient address it fails. See following string for general format

J_BLOGS/COMPANY_NAME/FROM1=OUR_COMPANY/FROM2=OUR_COMPANY/COV=template.rtf/NOTIFY=F/+441234567890@123.123.123.123

Can someone please advise me on how to configure sendmail to handle addresses of the above format.

Regards
John

If 441234567890@123.123.123.123 is an email address, you can't send an email to an ip address, it has to go to a domain name.
We stopped using real fax machines several years ago, and now use faxage.com.
Their service is about 65US per month, compared to 2 telephone lines at 40 per month plus the modems that were getting hard to find.
All you have to do is create an email with pdf attachments. The body of the email becomes the cover page, and the attachments are the fax. The email address is fax_number@faxage,com.
They return an email with the result.