FYI, I just received this email. I've been using Gmvault for a few years assuming it was abandoned, since there have been no commits since 2016, but thought I would create this issue anyway, just in case...

Hello,

Although you don’t need to take any action, we wanted to let you know that the following third-party apps will no longer be able to access some data in your Google Account, including your Gmail content. This change will go into effect starting March 31, 2019.

Gmvault

We are making this change as part of ongoing efforts to make sure your data is protected and private. These apps haven’t yet complied with our updated data privacy requirements announced on October 8, 2018.

You can always view, manage and remove apps you’ve given access to your account by visiting your Google Account.

Thanks,
The Google Accounts team