In the UK at least it you email agreeing to terms and then appear to be complying you're unlikely to get out of it.
Common examples are someone is sent a contract of employment unfortunately often after starting and they don't sign it. If they have been coming into work broadly in line with that contract so long as it's fair, employee and employer are bound by it.
Here is an interesting edge case in the UK [0]. Long story short if you give someone the ability to sign on your behalf and appear to consider parties bound by that it's binding.
In a personal sense, I send out appointment letters but my secretary does it for me. I consider myself as bound to that as if I arranged it myself. I gave the secretary latitude to book appointments for me, and I usually turn up to those appointments. If that letter is signed, or if it's by my hand. Doesn't legally matter as much as you'd imagine.
"An Englishman's word is his bond" as the old saying goes, verbal contracts are enforceable. The whole financial system used to run on purely verbal contracts. There are some requirements, there has to be a consideration for example. I am not sure this is true in other legal systems though.
I don't know about other places; but in the UK, a contract doesn't even have to be written down, let alone signed.
Of course, an unwritten contract is no more valuable than the paper it's (not) written on; and either party can dispute the terms. But you can still make a valid contract with a verbal agreement and a shake of hands. But don't do this unless you trust your co-contractor!
In most places, if there are witnesses to a contractual obligation being established or contract being performed, even a verbal agreement can be sufficient.
It mostly depends on how quickly courts will do the proceedings to establish that it is or isn't so.
Common examples are someone is sent a contract of employment unfortunately often after starting and they don't sign it. If they have been coming into work broadly in line with that contract so long as it's fair, employee and employer are bound by it.
Here is an interesting edge case in the UK [0]. Long story short if you give someone the ability to sign on your behalf and appear to consider parties bound by that it's binding.
In a personal sense, I send out appointment letters but my secretary does it for me. I consider myself as bound to that as if I arranged it myself. I gave the secretary latitude to book appointments for me, and I usually turn up to those appointments. If that letter is signed, or if it's by my hand. Doesn't legally matter as much as you'd imagine.
[0] https://www.lexisnexis.co.uk/blog/banking-and-finance/gordon...