App opens unrelated URLs

### Steps to reproduce
1. Open this link from Firefox on Android or an e-mail reader: https://seu.cleverreach.com/f/34891-164348/wss/269246-0630edf61ba28
2. Notice the link being opened in the Nextcloud app, or at least have it been shown as an option.
3.

### Expected behaviour
- Nextcloud doesn't care about unrelated, third-party URLs to marketing services

### Environment data
Android version: Android 11

Device model: Samsung Galaxy S10E, One UI 3.1

Stock or customized system: Stock, with Firefox for Android browser

Nextcloud app version: 3.18.1

Nextcloud server version: N/A

### Environment data
These URLs are apparently used for subscribing/confirming subscriptions for newsletters managed with cleverreach.com.