I do not put all the foes in the same initiative unless the dice fall that way. I think it is immensely unfair to the players when enemies are automatically bunched into the same block and will not bend on this.
I'm flexible in how I resolve posts in the same block and err on the side of what is in favor of the players. At a FtF table, if the Wizard likes to buff the party with haste, but is seated after the Fighter in initiative, the player would just ask the Fighter to delay. In PbP, that is a cumbersome option. Instead, if the Fighter is above the Wizard, but in the same block of initiatives (no enemies between them), I'll modify the rolls the Fighter made if the Wizard's spell would have changed it. If you aren't in the same initiative block, you'll have to declare your delay as normal.
I wait 24 hours from my previous post before putting characters into the next initiative block, effectively putting you in delay. This is not a punishment, I just like to keep combat moving so we don't spend a week on three rounds of combat due to slow posting.
An example:
Initiative
Biggy McSmasher <--- It would currently be this character's turn
Bad Guy
Bad Dude
Spellsy Mc Spells
I'm not a rogue
A DRAGON!
A whole 24 hours pass and there is not a word from the player. Time for delay!
Initiative
Bad Guy
Bad Dude
Biggy McSmasher <--- It would currently be all of their turns and the enemies turns were resolved
Spellsy Mc Spells <---/
I'm not a rogue <---/
A DRAGON!