exp — SPF Modifier
The SPF exp modifier lets you provide a custom human-readable explanation when SPF fails. Learn how to set it up and where it appears.
Type
Modifier
Modifier
Syntax
exp=<domain>
DNS Lookup
Yes — counts toward 10-lookup limit
Yes — counts toward 10-lookup limit
Example
exp=explain.example.com
💬 What This Modifier Does
The exp modifier lets you specify a domain whose TXT record contains a human-readable explanation of why SPF failed. This message may be included in NDR bounce messages returned to senders whose mail was rejected. It's used to provide helpful guidance, such as a link to your postmaster page or instructions for legitimate senders.
When to Use This
- Providing a helpful bounce message explaining why email was rejected
- Pointing senders to a postmaster page for delisting or contact
⚠️ Watch Out For
- Counts as one DNS lookup when an SPF failure occurs.
- Not all receiving MTAs surface the explanation in bounce messages.
- The explanation string supports SPF macros (%{d}, %{i}, etc.).
📚 RFC References
🔗 Related SPF Elements
🔧 Validate Your SPF Record
Check whether your current SPF record is valid and covers all your senders.