Using Email Attachments (iOS)

Good evening

I tried Using Email Attachments (iOS), I have an problem when I send an attachment by email my iphone sees the attachment as a text document even if the extension is custom and instead ask me if i launch my app i opens Directly into the mail file.

I noticed that the problem only occurs with certain mails like thunderbird, gmail sends me the attachment with my custom extension.

Can anyone help me?

Is this possible to open a TXT attachment in my app?

best regards