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Interesting problem. It is as others mentioned normal for a residential IP to be on RBLs. In fact, many of them request their ranges to be listed at spamhaus proactively because they have in their policies that customers shouldn't run mail servers on them. However, as you also noted, you're not running a mail server but your mail server is including your connecting IP in a Received header, and a content filter is checking Received headers against blacklists.
I've noticed an increase in this as well. One of my filter servers fell in a /24 that got SBL'd (cloud provider IP range) and we saw email rejections due to this, even though the filter server doesn't deliver the mail but merely passes it to the relays.
I think if this is going to be the trend, the email provider removing the client IP from the Received headers before sending it on isn't an unreasonable ask. It can be argued as a violation of accepted RFC standard, but standards are less important than working around unfair algorithms.
I would recommend bringing it to your mail provider with that request in mind: That they remove your IP from headers before sending the email on. It is the SMTP server that you connect to which writes that Received header, so it is the job of that server or one after it to remove it and it's not something you can influence withot their help. Unless of course you are running your own mail server, in which case I'd highly recommend removing a Received header before sending it on.
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