Sometimes misconfigured Imap/pop settings in yahoo mail server settings are offering you error and ensure that this settings matches with this settings:
For IMAP under Incoming Mail Server
Server – imap.mail.yahoo.com
Port – 993
Under Outgoing Mail Server (SMTP)
Server – smtp.mail.yahoo.com
Port – 587
Requires SSL – Yes
Requires Authentication – Yes
Logon Information
Email address – Enter your complete email address
Password – Enter your Password
Requires Authentication – Yes
For POP
Under Incoming Mail Server
Server – pop.mail.yahoo.com
Port – 995
Under Outgoing Mail Server (SMTP)
Server – smtp.mail.yahoo.com
Port – 465
Requires SSL – Yes
Requires TLS – Yes (in prompted)
Requires Authentication – Yes
Logon Information
Email address – Enter your complete email address
Password – Enter your Password
Requires Authentication – Yes
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