Personal letters, no matter the volume.
Generate a letter from an HTML template or upload a PDF. Mailstream prints, folds, stuffs, and mails it within 24 hours with full delivery tracking from press to mailbox.
Formats
Three sizes. One API.
Choose how your letter is assembled or let your code pick at send time. Single sheets, multi-page packets, window envelopes, and custom inserts, all with the same API and 24-hour turnaround.
Single-page letters
An 8.5×11" sheet, printed one- or two-sided, folded into a #10 envelope. Great for invoices and one-page correspondence.
Capabilities
Built for transactional and marketing mail alike.
- HTML or PDF input
- Design your letter in HTML with merge variables, or upload a pre-built PDF. Both render at 300 DPI for crisp, professional output.
- Merge variables
- Personalize every letter with recipient-specific data: names, account numbers, balances, dates, or any custom field your workflow requires.
- Batch sending
- Upload a mailing list and let Mailstream produce every letter in a single run. Thousands of letters, each uniquely personalized, processed overnight.
- Mail barcode tracking
- Every envelope is tracked from production through USPS handoff to delivery. Monitor status via the dashboard, API, or real-time webhooks.
- Address standardization
- Addresses are CASS-verified and standardized before printing. Bad addresses are flagged for correction before postage.
- Proof preview
- Review a rendered PDF proof of your letter before it prints. Approve individually or enable auto-approval for high-volume, template-driven sends.
Input
Personalization
Scale
Tracking
Deliverability
Quality
- 24hr
- Print-to-ship turnaround
- 6
- Max pages per envelope
- 300DPI
- Professional print resolution
- 100%
- Delivery tracking
- We are the manufacturer
- No middlemen or delays. Your mail goes directly from our floor to USPS, with quality checks.
- HITRUST-certified facility
- Your data runs in a HITRUST-certified environment with enterprise security and compliance.
- 25+ years of expertise
- Twenty-five years in direct mail, starting with an early online printer in 1998. We’ve tackled every edge case.
- Real-time USPS tracking
- Track Intelligent Mail barcodes. Know when printed, in transit, and delivered via dashboard, API, or webhooks.
Use cases
Physical letters for every business need.
- Invoices & statements
- Automate monthly statements and invoices for customers who require or prefer physical copies. Trigger sends from your billing system via API.
- Compliance & regulatory notices
- Healthcare EOBs, insurance notices, financial disclosures. When regulators require physical delivery, Mailstream handles the logistics.
- Onboarding kits
- Welcome new customers with a personalized letter, account details, and printed collateral. First impressions matter. Make yours tangible.
- Fundraising appeals
- Nonprofits see 3-5x higher response rates from direct mail than digital channels. Send personalized donation requests with return envelopes included.
Payload format
Predictable, typed JSON payloads.
Every webhook payload follows the same envelope structure. The nested data object contains the full mail piece resource at the time of the event.
What everyone is saying
Trusted by professionals.
We replaced three vendors with Mailstream and finally got full visibility from print to delivery. Tracking every piece in real time changed how we measure direct mail.
Daniel H.
VP of Growth, Northbridge Labs
The HTML design tool is a game changer. We design, personalize, and send without ever leaving the platform. No more emailing PDF proofs back and forth.
Olivia W.
Head of Lifecycle, Brightside
We integrated the API in a day and had automated compliance notices running by the end of the week. The HITRUST certification made our security team very happy.
Ethan K.
Engineering Lead, Cornerstone Health
Join agencies, SaaS teams, and operators using MailStream to automate direct mail at scale without manual vendors or guesswork.