Can't send email over cellular network from iPhone or iPad

Most email accounts involve 2 servers, one for incoming mail and a separate one for outgoing. You need to enter your username and password twice, once for the incoming server, and again for the outgoing (SMTP) server. If you are using WiFi on your ISP's network with some ISP's you don't need your username and password for outgoing, because it is entirely within their network. But you still need it over cellular data because they don't know who you are when using someone else's network. So most likely you have not entered the information for your SMTP server settings.

terrymchhi wrote:

I can send and receive email over wifi with no problems on both iPhone SE and iPad. If I disable wifi the internet connectivity is through the Verizon LTE network. Internet browsing is fine. Receiving emails is fine, but I cannot send an email through the Verizon LTE network on iPhone or iPad. My internet service provider is Time Warner Cable. I get the same behavior sending through an Apple iCloud email account.

Have you contacted Verizon, since you can't send using their cellular data service?

This is almost certainly an issue with your mail provider (TWC?).

Since you're not on their network (you're just some random cellular user as far as they are concerned), they are blocking your mail since you're likely to be a spammer.

Usually this is solved by configuring authentication with the SMTP server. This identifies you as a valid TWC customer, regardless of the network you connect via. Without knowing the specifics of TWC's service I can't be precise, but I'd look at Settings -> Mail -> accounts -> (your TWC account) -> Outgoing Mail Server and check the authentication settings.

terrymchhi wrote:

When I attempt to send an email with wifi disabled I get a message "Cannot send, user name or password for (my email address) is incorrect." Since everything works when on wifi, I know the user name and password are correct.

Thanks for your reply

Try deleting the email account and adding it back. This causes the device to download a new copy of the settings. It fixes a lot of things.

Is your wi-fi at home with TWC? If that is the case, the settings for using their network may be different than using the cellular network. Many times you get an error such as "does not allow relay". Check to make sure your account has SSL turned on if necessary in the SMTP server settings. Also, as Idris has indicated, removing and reinstalling the account may correct the issue. I would do this on the cellular network as opposed to wi-fi, which will make it easier to troubleshoot if you continue to have issues.

Camelot wrote:

This is almost certainly an issue with your mail provider (TWC?).

I agree but it is Verizon that's causing the problem and his home broadband provider is TWC. Here's what OP says:

I can send and receive email over wifi with no problems on both iPhone SE and iPad.

... Receiving emails is fine, but I cannot send an email through the Verizon LTE network on iPhone or iPad.

Sending out email through Verizon network require user authentication which can be easily fixed by entering username and password in the SMTP (outgoing) server settings.

Correction

Forget what I said earlier. It's TWC mail server that requires user to authenticate if they're trying to send out email from a network that doesn't belong to TWC. Sending out mail from home may not require authentication because user is in TWC network.

What happens when you try to send over cellular data? What the exact text of any error that you receive?