Failed to send attachments exceeding 750k

[ZGaopeng]

2021-01-28 15:58:21.252830+0800 用户端Demo[10183:3119213] S: 250 8BITMIME
2021-01-28 15:58:21.253096+0800 用户端Demo[10183:3119213] C: AUTH PLAIN AGF5YW5nY29vbDEwMEAxNjMuY29tAE1ITEhVT1BKVFZIUFBCT0g=
2021-01-28 15:58:21.287326+0800 用户端Demo[10183:3119213] ~~~~

235 Authentication successful
2021-01-28 15:58:21.287554+0800 用户端Demo[10183:3119213] S: 235 Authentication successful
2021-01-28 15:58:21.299214+0800 用户端Demo[10183:3119213] ~~~~

250 Mail OK
2021-01-28 15:58:21.299433+0800 用户端Demo[10183:3119213] S: 250 Mail OK
2021-01-28 15:58:21.309208+0800 用户端Demo[10183:3119213] ~~~~

250 Mail OK
2021-01-28 15:58:21.309415+0800 用户端Demo[10183:3119213] S: 250 Mail OK
2021-01-28 15:58:21.342167+0800 用户端Demo[10183:3119213] ~~~~

354 End data with .
2021-01-28 15:58:21.342375+0800 用户端Demo[10183:3119213] S: 354 End data with .
2021-01-28 15:58:21.609725+0800 用户端Demo[10183:3119213] ~~~~

421 Read data from client error
2021-01-28 15:58:21.609885+0800 用户端Demo[10183:3119213] S: 421 Read data from client error
2021-01-28 15:58:23.842890+0800 用户端Demo[10183:3119213] SocketStream read error [0x2834c61b0]: 1 54
2021-01-28 15:58:23.843495+0800 用户端Demo[10183:3119213] ~~~~
2021-01-28 15:58:23.843956+0800 用户端Demo[10183:3119213] S: