Since the update, I can't receive or send emails from T-Online?

What update? Have you verified your email server settings? According to the T-Online help site I found ( https://www.telekom.de/hilfe/apps-dienste/e-mail/posteingang-postausgang-server ), they should be these: IMAP incoming mail server: Server: secureimap.t-online.de Port: 993 Security: SSL POP3 incoming mail server: Server: securepop.t-online.de Port: 995 Security: SSL or TLS IMAP and POP3 outgoing mail server (SMTP): Server: securesmtp.t-online.de Port: 465 or 587 Security: SSL --------------- They note that "When setting this up in your email program, you will need an email program password." This is otherwise known as an "app password" and is not the same as your regular password for logging into their site. Sometimes a program update is seen by the provider as a new device, so a new app password may be required. App passwords can usually be generated at the provider's web mail page.