The sender mentions that since lightning uses disclosed secrets to invalidate old state, it is not necessary to keep every signature from the counterparty indefinitely. The email also mentions that RBF (Replace-By-Fee) has a minimum incremental relay fee of 1sat/vByte by default.

Regarding SIGHASH_SINGLE, it is stated that since it requires one output per input, combining multiple SIGHASH_SINGLE transactions together does not result in significant savings. Only 18 bytes are saved for nVersion, nLockTime, and the txin and txout size fields. On the other hand, the HTLC-timeout transaction is 166.5 vBytes, resulting in a savings of just 11%.

The sender brings up the scenario of needing to fee bump and add an additional input. In this case, the input takes up space and a change output is likely needed. The email suggests that using a pre-signed transaction may have been a better option in such cases.

Additionally, the sender mentions that the assumption of having many HTLCs in flight that need to be spent is often not the case.

The email includes a link to https://petertodd.org, along with the sender's email address: 'peter'[:-1]@petertodd.org.