Zoho gave me an IP address with no history this week. Senderscore.org says there's insufficient data to evaluate it. At other times Zoho has assigned me an email sending IP with a fair or good score.
I've seen less engagement with cold pitches this week. My domain checks out on email deliverability; I think it may be the IP or something else.
Are more of my emails likely going to spam because the sending IP doesn't have a history? I send a couple dozen pitches a week.
A lot goes into deliverability concerns, and you've found one of them: sender volume.
The major email players (Google, Microsoft, what's left of Yahoo) all use some in-house heuristics based on the kinds of traffic they've gotten from a given IP address. If your IP has very little traffic on it, they're going to be more suspicious of that traffic. This also ramps over time; if you get a new IP that has a lot of historic traffic, your low sending rates will degrade reputation over time.
This mechanic is one of several forcing mechanisms that urge small players to get a Google Apps/Office 365 account to send email, since those go out of a major player account with fairly solid reputation.
