SMTP Recipient Rejection: Should You Check the Domain or the Mailbox?
A 556 reply after RCPT may concern whether the target host accepts mail connections, rather than one individual mailbox. The reply timing and code identify the right first check.
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A 556 reply after RCPT may concern whether the target host accepts mail connections, rather than one individual mailbox. The reply timing and code identify the right first check.
Email authentication records work together. Identify your senders, test authentication and introduce a DMARC policy based on what your reports show.