Sometimes a certified IP address may experience a large and sudden increase or decrease in the number of Sender Reputation Data (SRD) votes it receives. This is because Microsoft commonly updates their SRD sampling algorithm in an effort to ensure accurate sample sizes of SRD votes.
Microsoft randomly and legitimately adjusts the numbers of SRD requests it sends to its users, prompting them to mark email as Junk or Not Junk.
For example, a certified IP may typically receive 10 SRD votes daily, however, with Microsoft's adjustment, it can suddenly increase to 40 votes. Alternatively, a certified IP that may typically receive 10 SRD votes daily can see a decrease in SRD votes to just 1 or 2 after an adjustment.
Sampling adjustments are typically temporary and usually do not last long. Senders should continue working on reducing their SRD Junk Votes as it impacts their IP reputation and their compliance within the Certification program.