Alias rules

Alias rules give you granular control over which incoming emails trigger your webhooks. Create rules to allow or block emails based on sender information and attachment characteristics.

Note: Rules are a Pro feature.

How rules work

Rules are evaluated before an email triggers your webhook. Each rule checks specific conditions and either allows or blocks the email.

Rule evaluation order:

  1. Block rules are evaluated first
  2. If any block rule matches, the email is rejected
  3. If no block rules match, allow rules are checked
  4. If allow rules exist and none match, the email is rejected
  5. If no rules exist, all emails pass through

Creating rules

Access rule settings

  1. Go to your alias settings
  2. Click on the "Rules" tab
  3. Click "Add rule"

Rule types

Allow rules

  • Only emails matching the criteria will trigger your webhook
  • Useful for restricting an alias to specific senders

Block rules

  • Emails matching the criteria will be rejected
  • Useful for filtering out unwanted senders or attachment types

Filter criteria

Sender email address

Filter by the sender's full email address.

Examples:

  • Allow only orders@supplier.com
  • Block spam@example.com

Sender domain

Filter by the sender's email domain.

Examples:

  • Allow all emails from @trusted-partner.com
  • Block all emails from @spam-domain.com

Attachment status

Filter based on whether the email has attachments.

Options:

  • Has attachments
  • No attachments

Use cases:

  • Only accept emails with attachments (for document processing)
  • Reject emails with attachments (for simple notifications)

Attachment file types

Filter based on attachment file extensions.

Examples:

  • Block .exe, .bat, .cmd (executable files)
  • Block .zip, .rar, .7z (compressed archives)
  • Allow only .pdf, .doc, .docx (documents)

Sender notifications

When an email is blocked by a rule, you can optionally notify the sender.

Enabling notifications

  1. Edit your rule
  2. Toggle "Notify sender when blocked"
  3. Optionally customize the notification message

Default notification

The sender receives a message explaining their email was not delivered due to filtering rules.

When to use notifications

  • When blocking senders who should know their email was rejected
  • For public-facing aliases where legitimate senders might be affected

When to skip notifications

  • When blocking obvious spam or unwanted sources
  • To avoid confirming your email address is active to spammers

Common configurations

Document processing alias

Only accept PDFs and Office documents:

Rule type: Allow
Criteria: Attachment file types
Values: .pdf, .doc, .docx, .xls, .xlsx

Trusted sender allowlist

Only accept from specific domains:

Rule type: Allow
Criteria: Sender domain
Values: @partner1.com, @partner2.com

Security block rule

Block potentially dangerous attachments:

Rule type: Block
Criteria: Attachment file types
Values: .exe, .bat, .cmd, .ps1, .vbs, .js

Internal-only alias

Only accept from your own domain:

Rule type: Allow
Criteria: Sender domain
Values: @yourcompany.com

Best practices

Start with block rules

Block unwanted content rather than trying to allowlist everything. This is more maintainable as your needs evolve.

Use domain rules over email rules

When possible, filter by domain rather than individual addresses. This handles new employees or email addresses automatically.

Test rules before going live

Send test emails from different addresses and with different attachments to verify your rules work as expected.

Combine with spam filtering

Rules work alongside spam filtering. Enable spam filtering for general protection and use rules for specific allow/block requirements.

Troubleshooting

Legitimate emails being blocked

  1. Check your rule order and logic
  2. Verify the sender address matches your criteria exactly
  3. Look for typos in domain names or email addresses
  4. Test by temporarily disabling rules

Rules not taking effect

  1. Ensure the rule is saved and enabled
  2. Check that you're on a Pro plan
  3. Verify the alias is correctly configured
  4. Allow a few minutes for changes to propagate

Sender not receiving block notifications

  1. Check that notifications are enabled for the rule
  2. The sender's mail server may be blocking the notification
  3. Some mail servers silently drop rejection notices

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