Like the "Automated Copyright Notice System" (http://www.acns.net/spec.html) except I don't think they went through any official standards body besides their own MPAA, or whatever.
I get circuits from several vendors and get maintenance notifications from them all the time. Each has a different format and each supplies different details for their maintenance. Most of the time there are core things that everyone wants and it would be nice if it were automatically readable so automation could be performed (i.e., our NOC gets the email into our ticketing system. It is recognized as being part of an existing maintenance due to maintenance id# (or new, whatever) and fields are automatically populated or updated accordingly.
If you're uncomfortable with the phrase "automatically populated accordingly" for security reasons then you can replace that with "NOC technician verifies all fields are correct and hits update ticket." or whatever.
The main fields I think you would need:
1. Company Name
2. Maintenance ID
3. Start Date
4. Expected length
5. Circuits impacted (if known or applicable)
6. Description/Scope of Work (free form)
7. Ticket Number