
In short, we do cold outreach because it's effective, it can produce results quickly, and, most importantly, it's extremely cost effective.
Before you get started, you should think about warming up a new email address so you don't run the risk of getting your main business domain/emails flagged as spam.
The easiest way to do this by following these steps:
1) Purchase a fresh domain. If your agency's domain is youragency.com, you could purchase something like youragency.co or your agency.mail, etc.
2) Create a GSuite account (visit gsuite.com and click "Get Started"), register the new domain in GSuite, then create an email for that domain in GSuite (something like mail@youragency.co). Note, GSuite charges $6/month per email address.
3) Sign up for 10-20 newsletters/services using the new email address so that emails start naturally flowing into the account. Here are some good ones: Twitter, Moz, Unbounce, Convince & Convert, The Daily Carnage, Neil Patel, Seth Goden, Buffer, Marketing Drive, Total Annarchy, Sketchalaytics.
4) Send 10-20 emails to friends/family and make sure they reply.
After a few days of emails going in and out of your new email account, the email address and domain will be "warmed up" and ready to go.