My Mac has begun to play up in Mail

Question

I have an iMac running 10.9.4.  My mail system has started being difficult.  It receives email but is progressively getting worse at sending them.  My system states
Cannot send message using server Sky
the sender address XXXXXXXXXXXXXXXX was rejected by the server smpt.tools.sky.com
The server response was: From address not verified - see http etc
select a different outgoing mail server from the list below or click try againLater to leave the message in your outboxuntil it can be sent
sending from MY EMAIL xxxxxx
it then has a box with 3 Sky options one with offline in barackets.
This morning we had 3 working accounts.  This evening I only have 1
Any help gratefully received as I am beginning to loose the will toi live.
Jeremy

Answer 1

Well here goes.
This message has not left my in box.
Jeremy
INITIATING CONNECTION Sep 03 23:53:22.166 host:smtp.tools.sky.com -- port:587 -- socket:0x0 -- thread:0x608001475dc0
CONNECTED Sep 03 23:53:22.613 [kCFStreamSocketSecurityLevelNone] -- host:smtp.tools.sky.com -- port:587 -- socket:0x6080004cd2e0 -- thread:0x608001475dc0
READ Sep 03 23:53:22.634 [kCFStreamSocketSecurityLevelNone] -- host:smtp.tools.sky.com -- port:587 -- socket:0x6080004cd2e0 -- thread:0x608001475dc0
220 smtp.tools.sky.com ESMTP ready
WROTE Sep 03 23:53:22.643 [kCFStreamSocketSecurityLevelNone] -- host:smtp.tools.sky.com -- port:587 -- socket:0x6080004cd2e0 -- thread:0x608001475dc0
EHLO [192.168.0.23]
READ Sep 03 23:53:22.667 [kCFStreamSocketSecurityLevelNone] -- host:smtp.tools.sky.com -- port:587 -- socket:0x6080004cd2e0 -- thread:0x608001475dc0
250-smtp.tools.sky.com
250-PIPELINING
250-SIZE 41697280
250-8 BITMIME
250 STARTTLS
WROTE Sep 03 23:53:22.667 [kCFStreamSocketSecurityLevelNone] -- host:smtp.tools.sky.com -- port:587 -- socket:0x6080004cd2e0 -- thread:0x608001475dc0
STARTTLS
READ Sep 03 23:53:22.691 [kCFStreamSocketSecurityLevelNone] -- host:smtp.tools.sky.com -- port:587 -- socket:0x6080004cd2e0 -- thread:0x608001475dc0
220 2.0.0 Start TLS
WROTE Sep 03 23:53:22.839 [kCFStreamSocketSecurityLevelTLSv1_0] -- host:smtp.tools.sky.com -- port:587 -- socket:0x6080004cd2e0 -- thread:0x608001475dc0
EHLO [192.168.0.23]
READ Sep 03 23:53:22.862 [kCFStreamSocketSecurityLevelTLSv1_0] -- host:smtp.tools.sky.com -- port:587 -- socket:0x6080004cd2e0 -- thread:0x608001475dc0
250-smtp.tools.sky.com
250-PIPELINING
250-SIZE 41697280
250-8 BITMIME
250 AUTH PLAIN LOGIN XYMCOOKIE
WROTE Sep 03 23:53:22.865 [kCFStreamSocketSecurityLevelTLSv1_0] -- host:smtp.tools.sky.com -- port:587 -- socket:0x6080004cd2e0 -- thread:0x608001475dc0
AUTH PLAIN  (*** 60 bytes hidden ***)
READ Sep 03 23:53:22.989 [kCFStreamSocketSecurityLevelTLSv1_0] -- host:smtp.tools.sky.com -- port:587 -- socket:0x6080004cd2e0 -- thread:0x608001475dc0
235 2.0.0 OK
WROTE Sep 03 23:53:22.989 [kCFStreamSocketSecurityLevelTLSv1_0] -- host:smtp.tools.sky.com -- port:587 -- socket:0x6080004cd2e0 -- thread:0x608001475dc0
MAIL FROM:<>
READ Sep 03 23:53:23.016 [kCFStreamSocketSecurityLevelTLSv1_0] -- host:smtp.tools.sky.com -- port:587 -- socket:0x6080004cd2e0 -- thread:0x608001475dc0
553 From address not verified - see http://help.yahoo.com/l/us/yahoo/mail/original/manage/sendfrom-07.html
WROTE Sep 03 23:53:23.016 [kCFStreamSocketSecurityLevelTLSv1_0] -- host:smtp.tools.sky.com -- port:587 -- socket:0x6080004cd2e0 -- thread:0x608001475dc0
QUIT