I've got a strange problem with a single mail sender (it is one of
those large free mail providers). My mail server works well with
thousands of senders but not this one, so we have made a connection
dump and it seems that the three way handshake is not completed

15:55:59.177431 IP ServerA.44601 > ServerB.25: S
2660877349:2660877349(0) win 5840 <mss 1380,sackOK,timestamp
3138006451 0,nop,wscale 0>
15:55:59.177751 IP ServerB.25 > ServerA.44601: S
4129790087:4129790087(0) ack 2660877350 win 5792 <mss
1460,sackOK,timestamp 2017496649 3138006451,nop,wscale 2>
15:56:02.972255 IP ServerB.25 > ServerA.44601: S
4129790087:4129790087(0) ack 2660877350 win 5792 <mss
1460,sackOK,timestamp 2017497598 3138006451,nop,wscale 2>
15:56:02.986696 IP ServerA.44601 > ServerB.25: . ack 1 win 5792 <mss
1460,sackOK,timestamp 2017497598 3138006451,nop,wscale 2>
15:56:02.986740 IP ServerB.25 > ServerA.44601: . ack 1 win 5792
<nop,nop,timestamp 2017497601 3138006451>
15:56:08.972156 IP ServerB.25 > ServerA.44601: S
4129790087:4129790087(0) ack 2660877350 win 5792 <mss
1460,sackOK,timestamp 2017499098 3138006451,nop,wscale 2>
15:56:08.987170 IP ServerA.44601 > ServerB.25: . ack 1 win 5792 <mss
1460,sackOK,timestamp 2017499098 3138006451,nop,wscale 2>
15:56:08.987192 IP ServerB.25 > ServerA.44601: . ack 1 win 5792
<nop,nop,timestamp 2017499101 3138006451>
15:56:20.972071 IP ServerB.25 > ServerA.44601: S
4129790087:4129790087(0) ack 2660877350 win 5792 <mss
1460,sackOK,timestamp 2017502098 3138006451,nop,wscale 2>
15:56:20.986619 IP ServerA.44601 > ServerB.25: . ack 1 win 5792 <mss
1460,sackOK,timestamp 2017502098 3138006451,nop,wscale 2>
15:56:20.986672 IP ServerB.25 > ServerA.44601: . ack 1 win 5792
<nop,nop,timestamp 2017502101 3138006451>
15:56:45.175830 IP ServerB.25 > ServerA.44601: S
4129790087:4129790087(0) ack 2660877350 win 5792 <mss
1460,sackOK,timestamp 2017508149 3138006451,nop,wscale 2>
15:56:45.190617 IP ServerA.44601 > ServerB.25: . ack 1 win 5792 <mss
1460,sackOK,timestamp 2017508149 3138006451,nop,wscale 2>
15:56:45.190664 IP ServerB.25 > ServerA.44601: . ack 1 win 5792
<nop,nop,timestamp 2017508152 3138006451>
15:57:33.375347 IP ServerB.25 > ServerA.44601: S
4129790087:4129790087(0) ack 2660877350 win 5792 <mss
1460,sackOK,timestamp 2017520199 3138006451,nop,wscale 2>
15:57:33.389931 IP ServerA.44601 > ServerB.25: . ack 1 win 5792 <mss
1460,sackOK,timestamp 2017520199 3138006451,nop,wscale 2>
15:57:33.389981 IP ServerB.25 > ServerA.44601: . ack 1 win 5792
<nop,nop,timestamp 2017520202 3138006451>


Someone can give me some advice? What I see is simply a strange mss
size at the beginning of 1380 that is not very usual but I am not sure
if it is relevant or not.