Email Address Validation

The validate command checks if email addresses are likely deliverable before you send emails. This helps prevent bounce-backs and improves email deliverability.

Overview

Email validation performs several checks to determine if an email address can receive messages:

1. Syntax validation - Checks if the email format is valid (RFC 5322 compliant)
2. Domain validation - Verifies the domain exists via DNS lookup
3. MX record check - Confirms the domain has mail server records configured
4. SMTP verification (optional) - Attempts to verify with the mail server directly

Basic Usage

# Validate a single email address
mailos validate user@example.com

# Validate multiple email addresses
mailos validate user1@gmail.com user2@outlook.com user3@company.com

# Using the --email flag (can be repeated)
mailos validate --email user@example.com --email another@domain.com

Command-Line Flags

Basic Options

Flag	Short	Type	Default	Description	Example
--email	-e	[]string		Email address(es) to validate (can be repeated)	mailos validate --email value

Advanced Options

Flag	Short	Type	Default	Description	Example
--full		bool	false	Perform full validation including SMTP check (slower)	mailos validate --full
--quick		bool	false	Perform quick validation (syntax + MX only)	mailos validate --quick

Output Options

Flag	Short	Type	Default	Description	Example
--json		bool	false	Output results as JSON	mailos validate --json
--verbose	-v	bool	false	Show detailed validation information	mailos validate --verbose

Command Flags

Flag	Short	Type	Default	Description
--email	-e	string[]		Email address(es) to validate (can be repeated)
--verbose	-v	bool	false	Show detailed validation information
--json		bool	false	Output results as JSON
--full		bool	false	Perform full validation including SMTP check (slower)
--quick		bool	false	Perform quick validation (syntax + MX only)

Examples

Basic Validation

$ mailos validate john@example.com

Email Address Validation Results
================================
Checked at: 2025-01-15 10:30:45

  john@example.com

--------------------------------
Summary: 1 valid, 0 invalid

Verbose Output

$ mailos validate andrew@happysoft.dev invalid@nonexistent-domain.xyz --verbose

Email Address Validation Results
================================
Checked at: 2025-01-15 10:30:45

  andrew@happysoft.dev
   Syntax: OK | Domain: OK | MX: OK
   Mail servers: in1-smtp.messagingengine.com, in2-smtp.messagingengine.com
   Details: Email address appears to be valid and deliverable

  invalid@nonexistent-domain.xyz - Domain does not exist
   Syntax: OK | Domain: FAIL | MX: FAIL
   Details: The domain 'nonexistent-domain.xyz' could not be found. DNS lookup failed.

--------------------------------
Summary: 1 valid, 1 invalid

JSON Output

$ mailos validate user@gmail.com --json

[
  {
    "email": "user@gmail.com",
    "is_valid": true,
    "syntax_valid": true,
    "domain_valid": true,
    "mx_valid": true,
    "deliverable": true,
    "details": "Email address appears to be valid and deliverable",
    "mx_records": ["gmail-smtp-in.l.google.com", "alt1.gmail-smtp-in.l.google.com"],
    "checked_at": "2025-01-15T10:30:45Z"
  }
]

Full SMTP Validation

For more thorough validation, use the --full flag which attempts to connect to the mail server:

$ mailos validate user@company.com --full --verbose

Note: SMTP verification can be slow and may be blocked by some mail servers. Many servers reject verification attempts for security reasons, so a failed SMTP check doesn't necessarily mean the address is invalid.

Integration with Send Command

Email validation is automatically enabled when sending emails. The send command will validate all recipients before attempting to send.

# Validation happens automatically (enabled by default)
mailos send --to user@example.com --subject "Hello" --body "Hi there"

# Skip validation if needed
mailos send --to user@example.com --subject "Hello" --body "Hi there" --no-validate

# Force send even if validation fails
mailos send --to user@example.com --subject "Hello" --body "Hi there" --force

# Enable SMTP verification during send
mailos send --to user@example.com --subject "Hello" --body "Hi there" --validate-smtp

Send Command Validation Flags

Flag	Type	Default	Description
--validate	bool	true	Validate recipient email addresses before sending
--no-validate	bool	false	Skip email address validation
--validate-smtp	bool	false	Perform SMTP verification during validation (slower)

Validation Results

Valid Email

When an email passes all checks:

• Syntax is correct
• Domain exists and resolves
• MX records are configured
• (Optional) SMTP server accepts the address

Invalid Email - Common Errors

Error	Description
Invalid email syntax	Email format doesn't match RFC 5322 standards
Domain does not exist	DNS lookup failed - domain may not exist or has expired
No mail server found	Domain has no MX records - cannot receive email
Recipient rejected	SMTP server explicitly rejected the address (full mode only)

Use Cases

Pre-Send Validation

Validate a list of recipients before a bulk send:

# Validate all recipients first
mailos validate user1@a.com user2@b.com user3@c.com

# If all valid, proceed with send
mailos send --to user1@a.com,user2@b.com,user3@c.com --subject "Newsletter" --file newsletter.md

Scripting and Automation

Use JSON output and exit codes for automation:

# Check exit code (0 = all valid, non-zero = some invalid)
if mailos validate user@example.com --json > /dev/null 2>&1; then
    echo "Email is valid"
else
    echo "Email is invalid"
fi

# Parse JSON output for detailed results
mailos validate user@example.com --json | jq '.[] | select(.deliverable == false)'

Cleaning Email Lists

Validate a list of emails and filter out invalid ones:

# Read emails from file, validate, and output valid ones
cat emails.txt | xargs mailos validate --json | jq -r '.[] | select(.deliverable) | .email'

Performance Notes

• Quick mode (--quick): Fastest, checks syntax and MX records only (~100ms per email)
• Default mode: Balanced, includes domain DNS verification (~200-500ms per email)
• Full mode (--full): Most thorough, includes SMTP verification (~1-5 seconds per email)

For bulk validation, consider using quick mode and only using full validation for critical addresses.

Limitations

1. SMTP verification is not definitive - Many mail servers block verification attempts or give false positives/negatives
2. Catch-all domains - Some domains accept all addresses even if the mailbox doesn't exist
3. Temporary failures - DNS or network issues can cause false negatives
4. Rate limiting - Validating too many emails quickly may trigger rate limits

Related Commands

• send - Send emails with automatic validation
• drafts - Create and manage email drafts
• search - Search for emails