E-mail marketing, transition to double opt in and 112% growth of the base

Basic Parameters
Mailings were sent approximately once a month through the MailChimp service (free tariff)
The mailing letter template did not match the brandbook.
There was no subscription confirmation.
There were 20 duplicated and unstructured subscriber databases.
It was possible to subscribe to the newsletter only through the subscription page on the website.

Accomplished
Moving to the Sendpulse mail service
Cleaning duplicates and transferring subscriber databases
The old databases were cleaned of invalid addresses
Implemented a two-stage subscription to the Double opt-in database
Added SPF and DKIM records
DMARC is configured
Status monitoring in Google, Mail.ru, Yandex is configured and performed
Implemented a subscription form for an invitation to become a subscriber in 1 click, which does not violate the Double opt-in rules
A wellcom email chain of 3 letters is configured
7 subscription forms were posted on the website
A pop-up form with a lead magnet that appears when leaving the site has been added
The mechanism of distributing additional materials through the subscription form and by auto-mail with a link to the material has been implemented five times
Micro-conversions on all forms in the analytics systems of Google Analytics and Yandex Metrics are configured

As a result
28 mailings were sent during 1.09.18 – 31.10.20
The increase of subscribers for the period 1.09.18 – 31.10.20 was: ≈112%
Unsubscribtions during 1.09.18 – 31.10.20 was: = 6.4%
Average OpenRate ≈ 26.7% (max: 34%)
Average number of clicks on links in the email: ≈3%