发送邮件出错

完整报错信息如下

2022-02-17 15:21:46     DEBUG   verifycode/verifycode.go:102    验证码  {"生成验证码": "{\"summer@example.com\":\"123456\"}"}
2022-02-17 15:21:46     DEBUG   mail/driver_smtp.go:27  发送邮件        {"发件详情": "{\"ReplyTo\":null,\"From\":\" \\u003c\\u003e\",\"To\":[\"summer@example.com\"],\"Bcc\":null,\"Cc\":null,\"Subject\":\"Email 验证码\",\"Text\":null,\"HTML\":\"PGgxPuaCqOeahCBFbWFpbCDpqozor4HnoIHmmK8gMTIzNDU2IDwvaDE+\",\"Sender\":\"\",\"Headers\":{},\"Attachments\":null,\"ReadReceipt\":null}"}
2022-02-17 15:21:46     ERROR   mail/driver_smtp.go:40  发送邮件        {"发件出错": "mail: invalid string"}
gohub/pkg/mail.(*SMTP).Send
        E:/Go/src/github.com/stringer/gohub/pkg/mail/driver_smtp.go:40
gohub/pkg/mail.(*Mailer).Send
        E:/Go/src/github.com/stringer/gohub/pkg/mail/mail.go:43
gohub/pkg/verifycode.(*VerifyCode).SendEmail
        E:/Go/src/github.com/stringer/gohub/pkg/verifycode/verifycode.go:70
gohub/app/http/controllers/api/v1/auth.(*VerifyCodeController).SendUsingEmail
        E:/Go/src/github.com/stringer/gohub/app/http/controllers/api/v1/auth/verify_code_controller.go:60
github.com/gin-gonic/gin.(*Context).Next
        E:/Go/pkg/mod/github.com/gin-gonic/gin@v1.7.7/context.go:168
gohub/app/http/middlewares.Recovery.func1
        E:/Go/src/github.com/stringer/gohub/app/http/middlewares/recovery.go:60
github.com/gin-gonic/gin.(*Context).Next
        E:/Go/pkg/mod/github.com/gin-gonic/gin@v1.7.7/context.go:168
gohub/app/http/middlewares.Logger.func1
        E:/Go/src/github.com/stringer/gohub/app/http/middlewares/logger.go:45
github.com/gin-gonic/gin.(*Context).Next
        E:/Go/pkg/mod/github.com/gin-gonic/gin@v1.7.7/context.go:168
github.com/gin-gonic/gin.(*Engine).handleHTTPRequest
        E:/Go/pkg/mod/github.com/gin-gonic/gin@v1.7.7/gin.go:555
github.com/gin-gonic/gin.(*Engine).ServeHTTP
        E:/Go/pkg/mod/github.com/gin-gonic/gin@v1.7.7/gin.go:511
net/http.serverHandler.ServeHTTP
        F:/GoLang/src/net/http/server.go:2879
net/http.(*conn).serve
        F:/GoLang/src/net/http/server.go:1930
2022-02-17 15:21:46     DEBUG   middlewares/logger.go:75        HTTP Access Log {"status": 200, "request": "POST /v1/auth/verify-codes/email", "query": "", "ip": "::1", "user-agent": "PostmanRuntime/7.29.0", "errors": "", "time": "6.843ms", "Request Body": "{\r\n    \"email\": \"summer@example.com\",\r\n    \"captcha_id\": \"captcha_skip_test\",\r\n    \"captcha_answer\": \"123456\"\r\n}", "Response Body": "{\"message\":\"操作成功\",\"success\":true}"}

环境：Win
出错之后，代码完全复制 7.6,7.7 教程的，还是一样的报错

安装完 Mailhog 不能直接启动，是使用完路径启动的：

$ $GOPATH/bin/MailHog.exe 
2022/02/17 15:25:38 Using in-memory storage
2022/02/17 15:25:38 [SMTP] Binding to address: 0.0.0.0:1025
[HTTP] Binding to address: 0.0.0.0:8025
2022/02/17 15:25:38 Serving under http://0.0.0.0:8025/     
Creating API v1 with WebPath:
Creating API v2 with WebPath:

想问下报错信息 mail: invalid string 是指哪个无效呢？