Using newer mail design then client version was never supported.   As part of our process we rolled out a modified bookmark.ntf that would redesign the mail file to the correct version and set an ini then done.    Short of this I would would either wait till all the clients are done or construct a view from the names.nsf and once you see a  client is upgraded you can redesign the mail file

When running the nconvert command I would use the -u option to convert all the folders to the latest design

Check out the desktop settings, there is a Mail Template Information section that you can use to specify what mail template to use for what release.  There are also check boxes that let you choose to upgrade the folder designs as well.  You can also have it notify you that the users template was upgraded.  It works very well.

I would bring down one Clustermate and run your convert with the Domino Server Down

Once the convert completes run the following...

(Assuming windows)

ndbmt.exe -updallThreads 8 -compactThreads 0

this will build all the critical mail views most users use so they don't have to wait for the views to be built when they first access after the design has changed...

Once this completes, bring Domino Server up and go to another Cluster Mate

Bring that server down and replicate it with the Server you already converted... If you just want to replicate mail directories that's fine

Again with server still down on 2nd Clustermate

ndbmt.exe -updallThreads 8 -compactThreads 0

once it completes bring Domino Server Up and then do same on last Clustermate..

If you want to start with just doing this on a single mail file to validate it to be safe that's always a good practice.. You can specify a database name or directory with dbmt

ndbmt.exe -updallThreads 1 -compactThreads 0 <database name>

Drop me an e-mail if you have any questions.  jpaganet@us.ibm.com

Regards,

John Pag

Replicate it with the one you upgraded

What you are looking for is a "Mail Template Upgrade Utility" (which we already have available)

This tool will check the person document on a regular basis and will replace the mail template based on configurable conditions.
E.g. if the client information in the administration tab in the person document contains at least one entry with 9.0.x , THEN ....

Rules can be combined, e.g. "and department = XYZ " , so you can plan your mail template rollout