Email outreach remains one of the most effective sales techniques, but, unfortunately, not all emails get successfully delivered. About 1% of your emails (to be precise, from 0.96% to 1.62% on average) will result in a bounce. And if at first glance the problem seems not that critical, with time, bounces hurt your sender reputation.
Problem 1: You send emails to invalid email addresses
If you are using a single opt-in, your email list may get filled with invalid email addresses as some new subscribers tend to put in fake emails or make spelling mistakes. Besides, invalid email addresses can appear in your database if you are following unhealthy lead generation practices, like purchasing email lists and not verifying the email addresses you've collected.