Pros:

1. One Sub-domain

You can set up one sub-domain in Mailgun for your marketing agency domain and use that same sub-domain for email sending across all of your client accounts in HighLevel

• Easy setup - only need to set up one subdomain for your domain which you already have access to
• Emails are white-labeled to your marketing agency domain or you can buy a generic domain so it will not show any agency branding

If your domain gets disabled (gets a bad score due to bounce rates) email will stop working for all of your clients since all of their accounts are powered by the same domain.

The solution: don't send spammy emails to poor email addresses :-)

2. Multiple Sub-domains

You can set up a subdomain in Mailgun for each of your client's domains and use that subdomain for sending for their specific HighLevel account. Once you set up a unique domain/subdomain for each location to capture cold inbound emails. Learn more about Cold Email Inbound Setup here.

• Emails are white-labelled per the client domain 
• If a client's domain gets disabled email only goes down for their client account

Difficult setup - time-consuming having to set up a subdomain for all of your clients and getting access to each of their domains