Hi
This is what I do:
1. takeaways: yes. If its up to £25 about £1 and over £30 I tip £2
2. supermarket delivery: yes about £2
3. DPD/Yodel/TNT etc: not at all
4. Postman: yes at Christmas
I think you're right about how that isn't logical but it does feel right.
I don't tip the postman when I have to sign for something so I wouldn't want to tip the DPD person (I have a better relationship with the postman than DPD!) but I DO tip the postman at Christmas.