"Offline points of sale" , but it still exists. put up a stand, roll-up or other banner in some shopping centers or business centers, which briefly describes the company and calls to subscribe to news or a newsletter. An option with zero return, but such an example really exists. The best example is the distribution of bonus or discount cards in exchange for filling out a questionnaire.
“Pull the base out of social networks” - for example, by registering for an event (webinar, seminar, participation in a drawing) on Facebook or Vkontakte.
"Interactive" — holding some kind of latest phone number database incentive events in a game form, the purpose of which is to collect a contact base. It can be anything. For example, you can rent a place in a shopping center, equip it with a photo zone and a printer for printing photos, invite passers-by to a photo shoot and give them printed photos in exchange for filling out a questionnaire. You can simply equip the zone and hand out samples of your products for free in exchange for filling out a questionnaire. You can organize some kind of voting on a topic that is very exciting for all subscribers in social networks (maybe it is the presidential elections or "betting on football teams" during a football match - whoever guesses the result first will receive a prize). You can offer to take a test. Prize drawings and competitions (exchange of a prize for a contact) occupy an important place in such events.
I have listed the most basic techniques for collecting an email address base. Of course, you can come up with more — there is no limit to your imagination. Now that the base has been collected, you can send out a mailing list using it, having created an email marketing strategy. But it is important to remember that the base should be constantly replenished with new clients, new incentive events, etc.
If your database has been lying around collecting dust for years and now you suddenly decide to send out a mailing, I don't recommend doing this. You need to work with the database constantly. But if you do decide to send out a mailing using this database that has never been used for mailings, you should at least check the addresses for working order using special services