Microsoft 365 Advanced Threat Protection VS Mimecast M2A License

A table of some of the added Features Mimecast can give you over Office 365 with ATP

POLICY 365 with Advanced Threat Protection 365 with Mimecast M2A
Impersontation Protection
Spam Filtering
URL ReWrite / Safelinks ✓ ( URL ReWrite is done at the time of receiving) ✓ ( Dynamic Rewrites )
Archive ✓ 7 second search SLA
Email Continuity ✓ ( C1 Product )
Signature Software
Disclaimer Software
DKIM
Attachment sandboxing ✓ ( SLA for Speed )
Safe File Conversion
Email encryption