Not MailGun, but we have 3 dedicated IPs with SendGrid and one problem is that there are spamlists and ISPs that block or mark down IP blocks owned by SendGrid

Not MailGun, but we have 3 dedicated IPs with SendGrid and one problem is that there are spamlists and ISPs that block or mark down IP blocks owned by SendGrid so you get no real advantage from the dedicated IP. I wish you could "bring your own IP" to these services.