Email API Comparison: Resend, SendGrid and MailBlastr

TL;DR

• Compare email APIs against your application's actual workload: message type, daily peaks, sending domains, event handling and operational support.
• Resend, SendGrid and MailBlastr have different current plan boundaries. A time-limited trial is not the same as an ongoing free allowance.
• MailBlastr currently supports HTTPS sending rather than a deployed direct SMTP listener. Include interface compatibility in the decision before comparing price.
• Run a controlled acceptance test and plan migration of suppressions, templates and events. A successful API response alone does not establish inbox placement or reliable operation.

Start with the workload, not a ranked list

An email API turns an application request into a managed sending workflow. The provider may handle submission, queueing and delivery events, while your application still decides who should receive a message, what it contains and how retries relate to the original business event.

Write down the workload before choosing a service. Are you sending password resets, receipts, newsletters or several distinct streams? How many messages are expected on a normal day and on the busiest day? How many domains, environments and customer accounts must remain separate?

This guide compares current public information from Resend, Twilio SendGrid and our own MailBlastr, checked in September 2026. It provides an evaluation method, not an independently measured deliverability ranking. No provider can establish your results solely through a feature table.

Compare current entry plans carefully

The table gives a starting point for checking eligibility and budget. Prices are advertised U.S. dollar monthly prices where shown; billing selection, taxes, additional features and overages can change the amount you pay.

Sources: Resend pricing, SendGrid trial documentation, SendGrid Email API pricing and MailBlastr's published plans.

Do not convert these rows into a universal “cheapest” winner. A domain limit, support requirement or necessary add-on can matter more than the entry price. SendGrid's displayed starting price does not by itself establish that every workload in the other rows has an identical included configuration.

Resend versus SendGrid: compare the workflow you will operate

For Resend, check how the transactional plan, marketing contacts, domain allowance and required webhook endpoints fit your application. Its pricing page separates these dimensions, so a team sending from many customer domains should inspect more than monthly email volume.

For SendGrid, check the Email API plan separately from Marketing Campaigns, along with the event history and account features you need. Its plan-upgrade documentation describes the trial ending after 60 days and a paid upgrade being required to continue sending. That distinction matters when comparing “SendGrid free plan” information found in an older tutorial.

Then evaluate the same scenarios in each candidate. Can you find the provider identifier for a failed receipt? Can you distinguish rejection from a later bounce? Can the team responsible for incidents access the necessary logs? A service can be a good fit for one operating model and an awkward fit for another.

Check API and SMTP compatibility early

If your application has a server-side HTTP integration, evaluate the provider's API and SDK. If an existing product only accepts SMTP settings, confirm a supported SMTP endpoint before assuming it can use an API key in a password field.

Resend documents a direct SMTP interface, and SendGrid's Email API pricing page lists SMTP and API support. MailBlastr currently provides HTTPS sending; its integration documentation states that raw SMTP listeners are not deployed.

That makes MailBlastr unsuitable as a drop-in SMTP hostname for an SMTP-only application in its current deployment. An application with a supported HTTP extension may still integrate through the API. Our SMTP connection guide explains the settings and the distinction in more detail.

Price normal volume and the busiest day

Prepare three scenarios: the current normal month, a plausible growth month and a short peak caused by a product event. Include transactional and marketing streams separately where the provider bills them differently.

For an original example, an application expecting 2,000 messages in a month may appear to fit a 3,000-message allowance. If 600 of those messages must be sent on launch day, a 100-per-day limit becomes the constraint. Delaying a password reset to stay inside an allowance is not equivalent to delaying a newsletter.

Also record overage behavior. Does sending stop, incur additional charges or require an upgrade? What happens to queued messages when the allowance is exhausted? Read the current terms and test a safe boundary condition if the provider offers an appropriate test environment.

Run an acceptance test with observable outcomes

Use recipients and domains you control or are authorized to test. Start with a small, clearly identified set of messages. Do not manufacture deliverability statistics from a handful of inboxes; the purpose is to validate your integration.

Record what was actually tested and what remains unverified. An advertised feature is useful evidence for a shortlist, but a successful controlled test is stronger evidence that your application uses it correctly.

Keep delivery reporting honest

An API acceptance event, receiving-server acceptance and a person's reading of the message are different observations. Avoid dashboards that label all three as “delivered to inbox.” The delivery diagnostic guide explains how to investigate missing mail without making that assumption.

Likewise, tracking events have limitations. Use a business outcome that matters to the workflow, such as completed verification or a successfully retrieved receipt, while protecting personal information and respecting the user's choices. See why open rates can mislead before comparing providers on that metric alone.

Plan the exit before moving production traffic

Keep templates, sender identities, suppressions and event mappings under your control. Decide how you will export or reproduce them if the service changes or no longer fits the workload.

For a migration, choose a small initial stream, record the old and new provider identifiers and define a rollback decision before moving more traffic. Preserve opt-outs and avoid replaying historical business events as fresh messages. The email migration checklist provides the operational steps.

Frequently asked questions

Is SendGrid still free?

Its current account documentation describes a 60-day trial, with a paid upgrade needed afterward to continue sending. Verify your account's actual plan rather than relying on older free-tier descriptions.

Is Resend free?

It currently lists a free transactional allowance of 3,000 emails per month with a 100-per-day cap. Check the current plan and the separate requirements for your marketing or add-on features.

Which email API has the best deliverability?

This guide does not establish a universal ranking. Sender practices, recipient behavior, content, authentication and the operating setup affect outcomes. Evaluate your own controlled workflow and ongoing evidence.

Should I migrate just to save on the entry price?

Only after considering compatibility, engineering effort, support, limits and migration risk. A lower advertised entry price is one input, not the whole decision.