How to solve email deliverability issues?

Question

Email Marketing

Hello!
I am a beginner email marketer. My colleague and I were assigned the task of outreach and cold mailings. We have been doing this for a couple of months now, but there are problems:
1) Very low delivery rate of letters, there are a lot of messages about the return and the inability to deliver the letter to the address, although the programmers insist that the DNS, DMARK, DKIM, SPF records are configured correctly.
2) The bounce rate has also increased recently, especially for a colleague. Almost all of her letters to valid addresses still go to the bounce.
3) Very low email open rates for the last 3 weeks.
Domains are not blacklisted, the unsubscribe link is in every letter and in a prominent place.
Most likely, some part of users still sent emails to spam.
The essence of the question is:
1) Is it possible to restore deliverability and how? Is it necessary to change the domain or just quarantine it (and how long can this last)?
2) What are the correct volumes for sending cold emails? Management insists on more than 1,000 emails per day to new addresses. I know that this is not right, I’m trying to prove my point of view, but so far they haven’t heard me (the management’s argument is that it works great for our competitors, which means I’m doing something wrong). I would like to choose the best option for the number and frequency of sending letters, which would suit both the management and allow us to keep the deliverability of letters at a high level for a longer time.
I know that such mailings are essentially spam, but the task is the task. And I want to do it in such a way that it is both effective and painless :)
I would be grateful to everyone for the advice.

Answer 1

"1233\n2345\n3467\n5677".split("\n") will return a String[] array with elements 1233 2345 and 5677 that can be inserted into 2D.