SMTP Server Information

AhaSend provides high-performance SMTP relay servers for sending transactional emails. Our SMTP infrastructure supports standard protocols and offers reliable email delivery with comprehensive error handling.

New to SMTP? Check out our SMTP credentials guide to get started, or try our HTTP API for a more modern approach.

Server Endpoints

AhaSend operates SMTP servers in multiple regions for optimal performance:

European Server

Hostname: send.ahasend.com
Location: Germany (Primary)
Best for: European and global traffic

US Server

Hostname: send-us.ahasend.com
Location: Oregon, USA
Best for: North American traffic

Server selection: Choose the server closest to your application for best performance. Both servers offer identical functionality and delivery capabilities.

Connection Settings

Supported Ports & Encryption

All AhaSend SMTP servers support the following configurations:

Servers: send.ahasend.com | send-us.ahasend.com
Ports: 25, 587, 2525
Encryption: STARTTLS (required)
Authentication: PLAIN (required)

SMTPS not supported: AhaSend does not support implicit SSL/TLS (SMTPS) on port 465. Use STARTTLS on ports 25, 587, or 2525 instead.

Authentication Requirements

Authentication Method: PLAIN authentication over STARTTLS
Username: Your SMTP username from the dashboard
Password: Your SMTP password from the dashboard
STARTTLS: Required for all connections

Get SMTP credentials: Create SMTP credentials in your AhaSend Dashboard in the “Credentials” page or via the API.

Connection Limits & Specifications

Understanding AhaSend’s SMTP limits helps you optimize your email sending:

Recipients Per Message

Limit: 50 recipients maximum per messageThis is the maximum number of consecutive RCPT TO commands that can be issued for a single SMTP transaction.

MAIL FROM: <[email protected]>
RCPT TO: <[email protected]>
RCPT TO: <[email protected]>
... (up to 50 recipients)
DATA

For bulk sending to more recipients, send multiple separate messages or use our HTTP API with batch operations.

Message Size Limit

Limit: 20 MB maximum per messageMessages exceeding this size will be rejected with an error code. This includes:

Email headers
Message body (text and HTML)
All attachments (base64 encoded)

Remember that attachments are base64 encoded, increasing their size by approximately 33%. A 15MB file becomes ~20MB when encoded.

Messages Per Connection

Limit: 10,000 messages maximum per connectionThis is the maximum number of consecutive MAIL FROM commands that can be issued for a single SMTP connection.When this limit is reached:

Additional MAIL FROM commands return transient failures
You should close and reopen the connection
Existing queued messages are not affected

Most SMTP libraries handle connection pooling automatically, but you may need to configure this for high-volume applications.

Connection Timeout

Timeout: 1 minute of inactivityConnections are automatically closed if there’s no new data within 60 seconds. This applies to:

Idle connections between commands
Slow data transmission during DATA command
Unresponsive clients

Keep connections active or implement proper reconnection logic in your application to handle timeouts gracefully.

SMTP Response Codes

AhaSend returns standard SMTP response codes with specific meanings:

Success Codes

Code	Description
`250`	OK - Message queued successfully for delivery

Error Codes

Code	Description	Action Required
`421`	Service Unavailable - This error could be returned as a result of disconnecting idle connections (idle too long), Load shedding (server is overwhelmed and cannot accept new connections), or temporary internal errors	Retry with exponential backoff
`451`	Internal server error - Temporary server issue	Retry the request
`500`	Invalid credentials - Authentication failed	Check username/password
`521`	Account disabled - Account suspended or out of credits	Check account status in dashboard
`552`	Invalid message format - Malformed email content	Validate email structure and headers
`553`	Email rejected - Recipient domain is toxic, temporary, or has typos	Verify recipient domain
`556`	Invalid account or domain - Account or sending domain not configured	Verify domain setup

553 email Rejection: This response is only returned if you enable Recipient Shields in your Account Settings.

Special Headers

AhaSend supports special email headers that modify system behavior:

Custom Headers

Learn about custom headers for tracking, routing, and advanced email features

Example Configurations

Basic SMTP Configuration

Host: send.ahasend.com
Port: 587
Security: STARTTLS
Username: your-smtp-username
Password: your-smtp-password
Authentication: PLAIN

Programming Language Examples

Node.js

Nodemailer and native SMTP examples

Python

PHP

PHPMailer and framework examples

Go

Native Go SMTP implementations

.NET

C# and .NET Core examples

Command Line

sendmail, swaks, and curl examples

Best Practices

Connection Management

Optimize your SMTP connections:

Reuse connections when sending multiple emails
Implement connection pooling for high-volume sending
Handle timeouts and reconnections gracefully
Close connections properly when done

Error Handling

Handle SMTP errors appropriately:

Implement exponential backoff for 421 responses
Retry 451 errors with reasonable delays
Don’t retry 5xx errors (permanent failures)
Log error codes for debugging and monitoring

Performance Optimization

Maximize sending performance:

Use persistent connections for batch sending (up to 10k messages per connection)
Choose the server closest to your application
Monitor connection limits and adjust accordingly

Security Considerations

Always use STARTTLS: Unencrypted SMTP connections are not secure and may expose your credentials and email content.

Credential Security

Store SMTP credentials securely
Use environment variables, not hardcoded values
Rotate credentials regularly
Use scoped credentials when possible

Domain Authentication

Verify your sending domains
Configure SPF, DKIM, and DMARC records
Use dedicated sending domains
Monitor domain reputation

Prefer HTTP API? While SMTP is great for compatibility, our HTTP API offers better performance, features, and error handling for modern applications.

Getting Started

Sending with SMTP

Sending with the API

Email Tracking

Integrations

Data Retention

Security

Scaling up

SMTP Server Information

Server Endpoints

European Server

US Server

Connection Settings

Supported Ports & Encryption

Authentication Requirements

Connection Limits & Specifications

SMTP Response Codes

Success Codes

Error Codes

Special Headers

Custom Headers

Example Configurations

Basic SMTP Configuration

Programming Language Examples

Node.js

Python

PHP

Go

.NET

Command Line

Best Practices

Security Considerations

Credential Security

Domain Authentication

Getting Started

Sending with SMTP

Sending with the API

Email Tracking

Integrations

Data Retention

Security

Scaling up

​Server Endpoints

European Server

US Server

​Connection Settings

​Supported Ports & Encryption

​Authentication Requirements

​Connection Limits & Specifications

​SMTP Response Codes

​Success Codes

​Error Codes

​Special Headers

Custom Headers

​Example Configurations

​Basic SMTP Configuration

​Programming Language Examples

Node.js

Python

PHP

Go

.NET

Command Line

​Best Practices

​Security Considerations

Credential Security

Domain Authentication

Server Endpoints

Connection Settings

Supported Ports & Encryption

Authentication Requirements

Connection Limits & Specifications

SMTP Response Codes

Success Codes

Error Codes

Special Headers

Example Configurations

Basic SMTP Configuration

Programming Language Examples

Best Practices

Security Considerations