So far, the Niantic support does only provide those categories for submitting requests (Copy+Paste):

• Request a nickname or team change
• Delete my Pokémon GO account
• Report an issue with a Gym or PokéStop
• Report inappropriate gameplay
• Report inappropriate Trainer behavior
• Report a bug
• Help with PokéCoins and premium items

There is no category who might fit in issues with changing mail address, but you may make a request anyway in e.g. the "nickname or team change" category and share your experiences.

So far, Niantic support only provides these categories for submitting requests:

• Request a nickname or team change
• Delete my Pokémon GO account
• Report an issue with a Gym or PokéStop
• Report inappropriate gameplay
• Report inappropriate Trainer behavior
• Report a bug
• Help with PokéCoins and premium items

There is no category that might fit in with issues around changing an email address, but you may make a request anyway in e.g. the "nickname or team change" category and share your experiences.