Feature Request: Get or apply Email Signatures

Is your feature request related to a problem? Please describe the problem.

At the moment, there is no API to obtain the (default) email signatures, so the user is forced to open a draft and add it manually.

Describe the solution you'd like.

We need access to the mailbox or user settings in order to retrieve all email signatures, so that new emails can be created with the corresponding signatures.

user.getMailboxSettings().getSignatures()

Additional context?

No response

该 issue 提议使用 user.getMailboxSettings().getSignatures()，但没有指出任何 repository 文件、测试或现有入口点。首先定位 Java SDK 中对 mailbox-settings 的支持，并确认底层 Microsoft Graph 能力；完成标准是 SDK 能够获取所有电子邮件签名，并具有测试覆盖率。