After poking around the database, it appears that the emails are correctly recorded as “sales <[email protected]>” and are being sent out with that string. When using an email formatted with a nickname the log shows only the nick name and not the full email unless you look at the raw header info. That led us to mistakenly believe that the domain was being dropped.
The case remains still though, Jetpack emails are not coming through to our inbox (nor our spam, nor our quarantine) while all other WordPress emails are. After spinning up a staging copy and changing the values in the database to the normal email format ([email protected]) rather than the nickname format and re-sending the problem emails they go through just fine.
It’s possible the issue lies somewhere else, in the chain, like the email server, but in the meantime is there a way to force Jetpack to use a traditional email address style rather than the “nickname” style?