https://lettr.com/blog/Lettr BlogGuides on email deliverability, transactional email and email infrastructure engineering.2026-10-06T00:00:00Zhttps://lettr.com/blog/lettr-mcp-server-tools/Manage an email platform from your AI assistant: Lettr's 79 MCP tools2026-10-06T00:00:00Z2026-10-06T00:00:00ZJack ZagorskiAn AI assistant such as Claude, ChatGPT, or Cursor can operate Lettr through 79 MCP tools, from sending and scheduling to campaigns, audience management, and delivery diagnostics, with more added as Lettr ships new features. This article covers what the tools do, the two ways to connect, and the guardrails that limit what an assistant can send or change.https://lettr.com/blog/mailgun-alternatives/5 best Mailgun alternatives for transactional email in 20262026-09-18T00:00:00Z2026-09-18T00:00:00ZJack ZagorskiFive Mailgun alternatives (Lettr, Mailtrap, Postmark, Amazon SES, and Twilio SendGrid) compared on log retention, free tiers, pricing at 50,000 and 100,000 emails a month, and traffic separation.https://lettr.com/blog/introducing-multilingual-campaigns/Introducing multilingual campaigns2026-09-16T00:00:00Z2026-09-16T00:00:00ZErik VlčákLettr campaigns can now send one email in several languages, and each contact receives the version that matches their language. This post covers which audiences benefit, what replaces the one-campaign-per-language setup, how messy language values like de-AT or german are handled, and what recipients see.https://lettr.com/blog/zaptime-cut-deliverability-tickets-to-zero/Zaptime cut deliverability tickets from dozens a month to zero with Lettr2026-09-11T00:00:00Z2026-09-11T00:00:00ZJack ZagorskiZaptime's customers were reporting that their clients never received booking confirmations, and Amazon SES gave the team no way to find out why. The switch to Lettr took a single day of engineering, and it came down to two things the alternative could not do: manage sending domains for hundreds of customer teams, and process data in the EU.https://lettr.com/blog/sendgrid-alternatives/5 best SendGrid alternatives for email delivery in 2026, compared2026-09-10T00:00:00Z2026-09-10T00:00:00ZJack ZagorskiFive SendGrid alternatives (Lettr, Mailtrap, Postmark, Amazon SES, and Mailgun) compared on free tiers, pricing at 50,000 and 100,000 emails a month, traffic separation, and what each one is actually good at.https://lettr.com/blog/why-lettr-runs-on-lambda-with-bref/Why Lettr runs on AWS Lambda with Bref2026-09-04T00:00:00Z2026-09-04T00:00:00ZJakub GauseWhy Lettr, a Laravel application, runs on AWS Lambda through Bref: the PHP runtimes and single-file deployment Bref provides, how Lettr's serverless.yml splits HTTP, queues, S3 events, and the scheduler into separate functions with no AWS keys anywhere, the Lambda limits we hit, and why Matthieu Napoli deserves the credit.https://lettr.com/blog/meet-adamko/Meet Adamko, Lettr's AI assistant2026-08-14T00:00:00Z2026-08-14T00:00:00ZErik VlčákAdamko is Lettr's built-in AI assistant. He sets up a new account from nothing but a website URL, creates branded templates and campaign drafts, diagnoses DNS and delivery problems from live account data, and records every change he makes in a team-wide activity log with one-click undo.https://lettr.com/blog/why-we-built-lettr-on-laravel/Why we built Lettr on Laravel2026-08-11T00:00:00Z2026-08-11T00:00:00ZJakub GauseWhy Lettr runs on Laravel and why our Laravel SDK is the most direct integration we offer: the defaults an experienced team would have picked anyway, the mail layer the SDK registers into as a native transport, the packages we run in production (Pest, Cashier, Bref, Spatie), the conventions that make a Laravel codebase legible to a coding assistant, and the community that has kept us on the framework since Laravel 4.https://lettr.com/blog/why-emails-go-to-spam/Why your emails go to spam (and how to fix it)2026-07-07T00:00:00Z2026-07-07T00:00:00ZErik VlčákA diagnostic guide to why emails go to spam: how spam filters actually decide, where to find the evidence (message headers, Google Postmaster Tools, Microsoft SNDS, blocklist checks), and the five causes behind most spam placement, each with the signs that identify it and the fix.https://lettr.com/blog/how-to-send-bulk-email/How to send bulk email the right way2026-07-04T00:00:00Z2026-07-04T00:00:00ZErik VlčákHow to send bulk email that reaches the inbox: the sending limits that rule out Gmail and Outlook mailboxes, the bulk sender requirements Gmail, Yahoo, and Microsoft now enforce, the legal rules in the US, EU, and Canada, and a six-step workflow from permission to monitoring.https://lettr.com/blog/what-is-an-email-api/Email API: what it is and how to choose one2026-07-01T00:00:00Z2026-07-01T00:00:00ZErik VlčákWhat an email API is and how it works: the request and response shape, how it differs from an SMTP relay and from mailbox APIs like the Gmail API, what an SMTP API means, the criteria that matter when choosing one, and the free tiers available in 2026.https://lettr.com/blog/best-transactional-email-services/Best transactional email services in 2026, compared2026-06-29T00:00:00Z2026-06-29T00:00:00ZErik VlčákA comparison of ten transactional email services (Lettr, Mailtrap, Postmark, SendGrid, Mailgun, Amazon SES, Resend, MailerSend, Brevo, SMTP2GO): current free tiers, pricing at 50,000 and 100,000 emails a month, deliverability track records, and which service fits which use case.https://lettr.com/blog/smtp-relay/SMTP relay: what it is and how to set one up2026-06-26T00:00:00Z2026-06-26T00:00:00ZErik VlčákWhat an SMTP relay is, how it differs from a mailbox SMTP server, how relay authentication and the TLS ports (465, 587, 2525) work, a step-by-step setup you can copy, and how a relay compares to IMAP and to a REST email API.https://lettr.com/blog/hard-bounce-vs-soft-bounce/Hard bounce vs. soft bounce: what email bounces mean and how to handle them2026-06-24T00:00:00Z2026-06-24T00:00:00ZErik VlčákWhat an email bounce is, the difference between a hard bounce (a permanent failure such as an address that does not exist) and a soft bounce (a temporary one such as a full mailbox), the common causes of each, why a bounce rate above roughly 2% damages sender reputation, and how to handle both kinds correctly.https://lettr.com/blog/mailer-daemon-mail-delivery-subsystem/Mailer Daemon and Mail Delivery Subsystem errors explained (and how to fix them)2026-06-19T00:00:00Z2026-06-19T00:00:00ZErik VlčákWhat a Mailer Daemon or Mail Delivery Subsystem bounce-back means, the common reasons an email fails to deliver, how to read the SMTP status code in the message, step-by-step fixes for each cause, Gmail and Yahoo specifics, and what bounces that arrive for mail you never sent are telling you.https://lettr.com/blog/email-attachment-size-limits/Email attachment size limits by provider (and how to send large files)2026-06-15T00:00:00Z2026-06-15T00:00:00ZErik VlčákThe attachment size limits for Gmail, Outlook, Yahoo, and iCloud Mail, why the real ceiling is lower than the number suggests because of encoding overhead, and the practical ways to send a file that is too big to attach, including large video.https://lettr.com/blog/onboarding-email-best-practices/Onboarding email best practices (with examples and templates)2026-06-12T00:00:00Z2026-06-12T00:00:00ZErik VlčákA practical guide to onboarding email sequences: what an onboarding email is, how to time and structure the welcome-to-activation flow, the best practices that matter (subject lines, personalization, a single CTA, the metrics to track), teardown examples, copy-paste templates, and how to send the sequence programmatically.https://lettr.com/blog/email-deliverability-checklist/Email deliverability checklist2026-06-09T00:00:00Z2026-06-09T00:00:00ZErik VlčákA complete email deliverability checklist covering authentication (SPF, DKIM, DMARC), list hygiene, content and spam triggers, sender reputation and IP warmup, and the monitoring metrics to watch, with a printable summary at the end.https://lettr.com/blog/email-signature-size-and-dimensions/Email signature size and dimensions2026-06-06T00:00:00Z2026-06-06T00:00:00ZErik VlčákThe recommended pixel dimensions, file size, and format for an email signature, how signatures render in Gmail, Outlook, and Apple Mail, and the common mistakes that make them break on mobile or load slowly.https://lettr.com/blog/introducing-lettr-marketing-audiences-and-campaigns/Introducing marketing emails in Lettr2026-06-02T00:00:00Z2026-06-02T00:00:00ZErik VlčákMarketing email now lives inside Lettr. The new module adds Audiences for managing who you send to and Campaigns for designing and sending bulk email, all in the same account and on the same domains you already use for transactional sending.https://lettr.com/blog/managing-lettr-from-your-ai-assistant/Managing Lettr from your AI assistant: the MCP integration2026-05-27T00:00:00Z2026-05-27T00:00:00ZErik VlčákHow Lettr's MCP integration lets an AI assistant call the Lettr API in plain language: what MCP is, what the tools cover, the difference between the remote and local servers, how to set up each one, and which tasks suit a chat interface versus the dashboard.https://lettr.com/blog/the-hidden-cost-of-diy-transactional-email/The hidden cost of DIY transactional email2026-05-13T00:00:00Z2026-05-13T00:00:00ZErik VlčákThe real cost of running your own transactional email stack: deliverability drift, no delivery logs, on-call time spent on bounces and blocklists, and template changes that require a deploy. What DIY actually costs beyond infrastructure, and what a managed alternative replaces.https://lettr.com/blog/how-to-warm-up-a-sending-domain/How to warm up a new sending domain2026-04-22T00:00:00Z2026-04-22T00:00:00ZErik VlčákHow to build sending reputation on a new domain by ramping volume gradually: who needs a warm-up, which recipients and content to send first, two sample ramp schedules, the bounce and complaint signals to watch, and the stop signals that mean pause immediately.https://lettr.com/blog/separate-transactional-and-marketing-email/Why you should separate transactional and marketing email2026-04-08T00:00:00Z2026-04-08T00:00:00ZErik VlčákWhy transactional and marketing email belong on separate subdomains: how shared sender reputation lets a marketing campaign drag 2FA codes into spam, how to classify the gray-area emails that sit between the two, and what the legal rules add on top.https://lettr.com/blog/smtp-vs-rest-api-how-to-choose/SMTP vs. REST API: how to choose and when to switch2026-03-18T00:00:00Z2026-03-18T00:00:00ZErik VlčákHow SMTP and REST API email transports differ in practice (statefulness, serverless fit, templates, idempotency, error handling), when each is the right choice, and a step-by-step plan for migrating from SMTP to a REST API.https://lettr.com/blog/spf-dkim-dmarc-explained-for-developers/SPF, DKIM, and DMARC explained for developers2026-03-04T00:00:00Z2026-03-04T00:00:00ZErik VlčákWhat SPF, DKIM, and DMARC each do, how they fit together to stop email spoofing, and how to read the DNS records and authentication headers to tell whether they're working.https://lettr.com/blog/the-journey-of-an-email/The journey of an email: from API call to inbox2026-02-18T00:00:00Z2026-02-18T00:00:00ZErik VlčákA step-by-step walkthrough of what happens to an email between your API call and the recipient's inbox: validation, message assembly, DKIM signing, DNS routing, the SMTP handshake, authentication, content filtering, and placement.https://lettr.com/blog/what-is-transactional-email/How transactional email actually works2026-02-04T00:00:00Z2026-02-04T00:00:00ZErik VlčákWhat separates transactional email from marketing email, why inbox providers and regulators treat them differently, and how to keep these messages reliable in production.