Quite an engaging and fun method of growing one's email list is running a contest or giveaway. Users have to enter the contest using their email addresses. Just make sure the prize you offer resonates with your target audience and aligns with your business.
4.4 Hashtags and Social Campaigns
Other ways could be to run a hashtag campaign
Germany Email Database on Twitter or Instagram where individuals are encouraged to share content and, in turn, sign up with one's brand for exclusive offers via email. 5. Influencer Marketing and Partnerships
Another effective way to grow your email list is by collaborating with influencers or industry leaders in your niche. Influencers already have access to a huge, targeted audience you can tap by offering them an exclusive deal or some sort of content in return for their email address .
How to do it:

Guest Blogging or Sponsored Content: It may be writing a guest blog or sponsoring the content of influencers; you give them valuable resources in return for email sign-ups.