Bond keeps what you tell it about the people you care about: their name, how you know them, the dates that matter to them, notes of what you talked about, promises and plans, gift ideas, what they are into, and how often you want to be in touch.
Everything about a person is locked with your account's own key before it is stored. In Bond's records, the only things readable without that key are your account id, random row ids, the times rows were written, and a version number. There is no name, no date, no relationship and no note in the clear — so a stolen copy of Bond's records cannot say whose they are, or who they are about.
The same friend in two people's Bonds shares nothing: the two are unrelated records with nothing in common.
Bond writes to someone only the way you choose. A message to someone in your life goes by email through Memriq's mail service, from "<your name> via Bond", with replies going to you. At the default it stops at a draft you approve under Messages; if you let Bond send on its own, every message it sent is listed there with whether it arrived.
Your email. If you connected your email in Helm, Bond looks there only when you press "Look now", and only for messages that mention someone in your Bond. The message itself is read and then discarded — never stored, logged or shown. If it says something worth keeping ("her project ended this week"), Bond shows that as a proposal with who sent it, the subject and the date, and keeps it only if you press Keep.
Forget this person deletes the person and everything Bond keeps about them, and any reminders Bond put in your Helm for their dates. Settings › Your data lets you download everything Bond keeps, or delete it all.