SendGrid is enterprise-scale email infrastructure with Inbound Parse. MCPmailer is a per-agent mailbox with MCP tools and oversight.
Transactional email APIs · SendGrid claims checked July 2026
SendGrid, now part of Twilio, is one of the largest senders on the internet: marketing and transactional in one platform, Inbound Parse for receiving, IP pools, subusers for tenancy, and the compliance paperwork a large company expects to be handed.
If you are standardised on Twilio, need marketing and transactional under one contract, or need dedicated IPs and subuser isolation at scale, keeping everything in SendGrid is a defensible call.
SendGrid is sized for volume, not for conversation. Inbound Parse gives you a POST body, subusers give you tenancy rather than agent identity, and nothing in the product models a thread, a wait, or an approval. Since the permanent free tier ended in 2025, a small agent experiment also starts at a paid plan.
A subuser separates billing and reputation between parts of your business. An agent identity is smaller and sharper: one address, one key, its own audit trail, invisible to the other agents in the workspace. Ten agents should be ten revocable keys, not ten configuration exercises.
Inbound Parse posts the message with limited routing rules on top. Which thread it belongs to, what was said before, and whether this person already asked to be left alone are all questions you answer from your own store. We answer them on ingest, and expose the answers as tools.
SendGrid moved to a 60-day trial in 2025. Ours is 3,000 emails a month, 100 a day, three inboxes, no card, with receiving and threading included, which matters when you are still deciding whether an agent with an inbox is a good idea at all.
Every row is a claim we could defend with their documentation open beside it. Where they are ahead, the row says so.
The marketing and transactional volume has no reason to move.
Keep campaigns and transactional where they are
Contact lists, templates, and analytics are not things we do.
Give agents a separate subdomain
Agent sending stays off the domain and IPs your bulk mail has warmed.
Replace the Parse endpoint for agent addresses only
Route those addresses here and let the agent use tools instead of your webhook.
You can point addresses at Inbound Parse and separate keys with subusers, but the mailbox, the thread, the history, and the audit trail are all things you build on top.
The permanent free tier ended on 27 May 2025 and was replaced by a 60-day trial. Ours is a standing 3,000 emails a month with no card.
For an agent that only sends notifications at high volume, yes. For one that holds conversations, you are building the conversation layer yourself.
Available here as an add-on on higher plans, and free sending is isolated on a separate pool by default so it cannot affect paid delivery.
Keep your transactional sender for the mail your product sends. This is for the addresses your agents converse from, which is a different job with different failure modes.
The free tier is 3,000 emails a month across three agent inboxes, no card, with receiving, threading, and search included. Enough to watch a real conversation happen before you decide.
More Transactional email APIs