Civilization 5 does not support Play by Email

A quick search of the Manual finds that there are two multiplayer modes:

• Local Area Network
• Internet/Steam

Now you're thinking you can just start a multiplayer game and email the save file? There's a big problem preventing that:

Simultaneous Turns Games

A multiplayer game is a “simultaneous turns game.” In this style of game, you and your opponents take their turns simultaneously. Everybody moves units, conducts diplomacy, maintains their cities all at the same time. When everybody’s done everything they want to do, the turn ends and another begins. You can use a Turn Timer when playing in this format as well. Simultaneous Turns games can be a whole lot of fun, but they’re not for everybody. We recommend that you get a bunch of practice in turn-based Civ V before you jump into a simultaneous game.

You won't both be able to take turns.

Overall, I don't believe Play By Email is possible yet in Civ 5.

EDIT: Evidence! They would like to add it soon. Source

About a month after release, we’re going to add Pitboss. Pitboss will be accompanied by two extraneous modes that we weren’t originally planning, but the fans keep asking for: play-by-mail and hot-seat.

Civilization 5 does not yet support Play by Email

However, they would like to add it soon. Source

About a month after release, we’re going to add Pitboss. Pitboss will be accompanied by two extraneous modes that we weren’t originally planning, but the fans keep asking for: play-by-mail and hot-seat.

A quick search of the Manual shows the only play modes supported right now are:

• Local Area Network
• Internet/Steam

Now you're thinking you can just start a multiplayer game and email the save file? There's a big problem preventing that:

Simultaneous Turns Games

A multiplayer game is a “simultaneous turns game.” In this style of game, you and your opponents take their turns simultaneously. Everybody moves units, conducts diplomacy, maintains their cities all at the same time. When everybody’s done everything they want to do, the turn ends and another begins. You can use a Turn Timer when playing in this format as well. Simultaneous Turns games can be a whole lot of fun, but they’re not for everybody. We recommend that you get a bunch of practice in turn-based Civ V before you jump into a simultaneous game.

You won't both be able to take turns. As far as I can tell, you'll have to wait till they add support.

Civilization 5 does not support Play by Email

A quick search of the Manual finds that there are two multiplayer modes:

• Local Area Network
• Internet/Steam

Now you're thinking you can just start a multiplayer game and email the save file? There's a big problem preventing that:

Simultaneous Turns Games

A multiplayer game is a “simultaneous turns game.” In this style of game, you and your opponents take their turns simultaneously. Everybody moves units, conducts diplomacy, maintains their cities all at the same time. When everybody’s done everything they want to do, the turn ends and another begins. You can use a Turn Timer when playing in this format as well. Simultaneous Turns games can be a whole lot of fun, but they’re not for everybody. We recommend that you get a bunch of practice in turn-based Civ V before you jump into a simultaneous game.

You won't both be able to take turns.

Overall, I don't believe Play By Email is possible yet in Civ 5. I recall hearing they plan to expand lots of multiplayer options in coming patches. (Now I could just find a reference to that) We can hope Play By Email is added that way.

Civilization 5 does not support Play by Email

A quick search of the Manual finds that there are two multiplayer modes:

• Local Area Network
• Internet/Steam

Now you're thinking you can just start a multiplayer game and email the save file? There's a big problem preventing that:

Simultaneous Turns Games

A multiplayer game is a “simultaneous turns game.” In this style of game, you and your opponents take their turns simultaneously. Everybody moves units, conducts diplomacy, maintains their cities all at the same time. When everybody’s done everything they want to do, the turn ends and another begins. You can use a Turn Timer when playing in this format as well. Simultaneous Turns games can be a whole lot of fun, but they’re not for everybody. We recommend that you get a bunch of practice in turn-based Civ V before you jump into a simultaneous game.

You won't both be able to take turns.

Overall, I don't believe Play By Email is possible yet in Civ 5.

EDIT: Evidence! They would like to add it soon. Source

About a month after release, we’re going to add Pitboss. Pitboss will be accompanied by two extraneous modes that we weren’t originally planning, but the fans keep asking for: play-by-mail and hot-seat.