On Sat, Oct 16, 2021 at 2:35 PM Dave Crocker via mailop <mailop@mailop.org> wrote:
> > > On 10/15/2021 5:40 PM, Grant Taylor via mailop wrote: > > The motivation for spreading service IPs across different /24 prefixes > > is so that if > > The issue here is not the generic one of using multiple IPs. It is > about using them to separate IMAP from SMTP. That's an entirely > different matter. > > To the extent that anyone claims that there is a reptuation-related > reason for this kind of separate, for this kind of service distinction, > they need to provide substantial detail that makes the validity of the > reason crystal clear. > I have not seen it specifically for IMAP and SMTP, but I have seen it for SMTP and HTTP. Specifically, I've seen people block http(s) access to an A record based on a hostname pointed at it being advertised in spam or if the smtp server and web server are shared, ie they don't block by port instead, they use a broad block in both directions. I wouldn't be overly worried about it for IMAP, given that your IMAP customers are likely quite different than who they are mailing, so it seems the likely overlap of those blocks is going to be small. Brandon
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