My SIL is lovely and I get on very well with her. She doesn't have a permanant address for reasons I won't go into and so has difficulty in receiving mail.
For a while MIL has been redirecting SIL's mail to our address as we live closer to her. Not overly happy about it but I keep out of it and DH passes the mail on when we see her. Anyway, this morning a letter arrived at our address to SIL from HMRC - clearly addressed to her at our address. I've just opened it as assumed it was for me and it relates to her self-assessment. Am I being unreasonable in not wanting SIL to use our address with HMRC? I don't think I am but other opinions welcome!!