Why is there so much outbound traffic from Airmail 3 (from Bloop)?
Privacy Policy and EULA

You should read Bloop SRL's Privacy Policy and End User Licence Agreement.

Bound by the GDPR

As an Italian organisation, based within the European Union, Bloop SRL is bound by the General Data Protection Regulation which should give you some reassurance.

No absolutes

However, no-one here can answer with absolute certainty that you can trust your information with the organisation. Policies and organisations can and do change.