Which of the following items is a requirement that bulk senders must meet in order for Gmail and Yahoo to pass your messages to the inbox?

Gmail and Yahoo require bulk senders to authenticate their emails using both DKIM (DomainKeys Identified Mail) and SPF (Sender Policy Framework). These authentication methods verify that the email truly originated from the domain it claims to be from, preventing spoofing and phishing attempts. Failing to pass these checks significantly increases the likelihood of emails being delivered to spam or rejected entirely. While including a manage preferences link is a best practice for deliverability and compliance, it is not a mandatory technical requirement for inbox placement by Gmail and Yahoo. Limiting image files is not a direct requirement for inboxing; email content and size can influence deliverability, but there's no strict "one image" rule.