Your instance has data covered by GDPR, but the data it sends to other instances is covered by the same exceptions as the data you send in a email. Without exceptions for legimitate interests it would be illegal to send an email from, say, mailbox to Gmail or Yandex Mail.
Your instance has data covered by GDPR, but the data it sends to other instances is covered by the same exceptions as the data you send in a email. Without exceptions for legimitate interests it would be illegal to send an email from, say, mailbox to Gmail or Yandex Mail.