Search contacts by phone number


Yep, you heard it right. I know it’s a wild idea.
But with Delta Chat becoming more and more normie-friendly (e.g. instant onboarding) I thought I’d shoot my shot.

Why it’s important

We know that practically every messenger including Signal uses phone numbers to look for contacts.

All family members usually have each other’s phone number, unlike, let’s say, Instagram or Snapchat or email address.
So when you aren’t, want to connect with you on a messenger, all you have to do is to tell her, “install WhatsApp” or “install Telegram”, and after that she’ll automatically have you in her contacts list.

In addition, it’s pretty cool to find out who from your contacts is using Delta Chat, like it is with Signal.

The implementation

Yes, this will probably require a central server that stores the email to phone number associations DB, but it could also be a part of one particular email server like And perhaps the phone numbers could be queried from multiple servers, multiple databases.

When the user first logs in or creates an account, we aske them to (optionally) enter their phone number. Then we store it in the database.

More thoughts

Perhaps this doesn’t even have to be integrated in Delta Chat directly. It could be a separate app that modifies the contacts on any person’s phone by adding the email address to each contact (Though perhaps you can’t exchange keys this way)

Some companies specialize in maintaining phone to email databases:

A wild idea indeed! Personally I am against this idea and offer my thoughts below, but maybe other people find it convenient and want to weigh in with their own thoughts.

Personally I like the fact that Delta Chat is not like Signal and never asks for my phone number. Apps like Signal are not good role models to imitate. One of Signal’s longest standing complaints from users relates to its reliance on phone numbers.

For some people this is cool, other people have long despised this “feature”.

Sounds like a privacy nightmare.

I think this setup can be abused by bad actors to carry out MITM attacks.

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if it was that easy it I would added that feature to DeltaLab long ago, the problem is that you can’t trust the phone number user enters, you need to verify they own the phone number doing verification via SMS code, like all other messengers you mentioned do, this costs money, and will cost more and more money as Delta Chat becomes more popular, for a business that is making profits it is an inversion, for Delta Chat it is all loses

Right, missed that part.

Well, Delta Chat has funding, so does Signal.

why should we spend funding money on sms verifications? I doubt we could even use it for that purpose as it is mostly purpose bound to pay for development.

Also sms verification also has many complexities and risks, remember the twilio incident?

Maybe someone wants to make a bot or companion app for that, but I personally can not really think of a good solution that deltachat could integrate by default.
Or another thing that someone could build is an email provider where you can register with your phone number, try to login with phone number, get an sms with a one time password. a bit vulnerable and dumb IMO, but could be nice for people that don’t want to remember passwords and can life with the risk of sim-highjacking.