We have two email servers for redundancy (like when Gmail is rate-limiting), not load. We send about 10,000 messages a day total, or about seven per minute, spr

We have two email servers for redundancy (like when Gmail is rate-limiting), not load. We send about 10,000 messages a day total, or about seven per minute, spread fairly evenly across the day. No mass email. I suppose it would be an interesting exercise to slowly increase servers/IP addresses until rate limiting stops, but servers cost time and money.