Can't send emails from webmail

[Trinny5]

Receiving emails on Talktalk webmail but unable to send emails.

I get this message:

Message could not be sent to the following recipients: [t........@gmail.com) (453 - 453 4.2.0 vYvCpxnhzqmMi Too Many Recipients (TT605)

Tried in Outlook and recieved this message:

Cannot Send mail

The server rejected one of the recipients addresses. The message has been plaved in your outbox.

This started yesterday morning.

Previously no problem sending to the addresses I tried yesterday.

[Michelle-TalkTalk]

Morning,

I'm sorry for the delay. Would it be possible to retest and confirm if this is still happening please?

Thanks