How to add a logo to the avatar slot alongside emails from Marketing Cloud

Hi, I'm working in a Ukrainian NGO. Last year, we started working with SalesForce CRM and recently integrated the Marketing Cloud Module. Now, we use Marketing Cloud for all emails, and unfortunately, our logo is not displayed in emails, although we had it before while using another email service.

One reason mentioned is that we need VMC (Verified Mark Certificate) to display the registered trademark logo in the avatar slot alongside outgoing emails. VMC is a paid certificate, and we are trying to find an alternative way how to add the logo to emails. 

Would be grateful if anyone had the same experience and could help with this issue.