Where do I find my selector?

In the DKIM-Signature header of a message you sent (the s= tag), or in your email provider’s DKIM settings.

What key size should I use?

2048-bit RSA is the norm today. 1024-bit keys still validate but are considered weak.

DKIM Check

DKIM (DomainKeys Identified Mail) signs outgoing email with a private key and publishes the matching public key in DNS under a selector. This check fetches the key for a selector, or probes common selectors, and reports its type, size, and test mode.

When to use this: You are setting up a new sender, or messages fail DKIM or show dkim=none in their headers. Command prefix dkim:

About the DKIM Check

Look up a DKIM public key by selector, or probe common selectors to find the keys a domain publishes, and check key type, size and test mode.

FAQ

Where do I find my selector?: In the DKIM-Signature header of a message you sent (the s= tag), or in your email provider’s DKIM settings.
What key size should I use?: 2048-bit RSA is the norm today. 1024-bit keys still validate but are considered weak.