Email sending and authentication issues

I have two problems. First, I can receive but not send emails. On sending I get a message “invalid length for a Base-64 char array”. This even when trying a test email of only a few words. Second, I changhed my password (which subsequently let me into this convetsation site) but when trying to send an email I get a second message “authentication failed” even after I have updated the password using “tools”>“accounts”. Help please.

Hi, what version of eM Client are you currently using? Can you please make a screenshot of the error you’re seeing? What mail service are you using?
How did you setup the account?

Thank you,